diff --git a/src/main/java/com/sztzjy/linkCommerce/controller/stu/StudentTrainingAnswerController.java b/src/main/java/com/sztzjy/linkCommerce/controller/stu/StudentTrainingAnswerController.java
index 7712397..9c669bd 100644
--- a/src/main/java/com/sztzjy/linkCommerce/controller/stu/StudentTrainingAnswerController.java
+++ b/src/main/java/com/sztzjy/linkCommerce/controller/stu/StudentTrainingAnswerController.java
@@ -32,6 +32,8 @@ import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepOneValidationRe
 import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepOneValidationResult;
 import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepTwoValidationRequest;
 import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepTwoValidationResult;
+import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepThreeValidationRequest;
+import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepThreeValidationResult;
 import com.sztzjy.linkCommerce.service.NewProductSurveyStepOneService;
 import com.sztzjy.linkCommerce.service.MarketOpportunitySelectionStepOneService;
 import com.sztzjy.linkCommerce.service.MarketOpportunitySelectionStepTwoService;
@@ -46,6 +48,7 @@ import com.sztzjy.linkCommerce.service.ProductDevelopmentFactorsStepThreeService
 import com.sztzjy.linkCommerce.service.ProductDevelopmentFactorsStepFourService;
 import com.sztzjy.linkCommerce.service.BusinessFeasibilityStepOneService;
 import com.sztzjy.linkCommerce.service.BusinessFeasibilityStepTwoService;
+import com.sztzjy.linkCommerce.service.BusinessFeasibilityStepThreeService;
 import com.sztzjy.linkCommerce.service.StudentTrainingAnswerService;
 import com.sztzjy.linkCommerce.util.ResultEntity;
 import io.swagger.annotations.Api;
@@ -103,6 +106,9 @@ public class StudentTrainingAnswerController {
     @Autowired
     private BusinessFeasibilityStepTwoService businessFeasibilityStepTwoService;
 
+    @Autowired
+    private BusinessFeasibilityStepThreeService businessFeasibilityStepThreeService;
+
     @GetMapping("/{taskKey}")
     @ApiOperation("查询当前学生指定实训任务答案")
     public ResultEntity<StudentTrainingAnswer> detail(@PathVariable String taskKey,
@@ -285,6 +291,17 @@ public class StudentTrainingAnswerController {
         }
     }
 
+    @PostMapping("/business-feasibility/step-3/validate")
+    @ApiOperation("商业可行性论证第三步校验")
+    public ResultEntity<BusinessFeasibilityStepThreeValidationResult> validateBusinessFeasibilityStepThree(
+            @RequestBody BusinessFeasibilityStepThreeValidationRequest answer, HttpServletRequest request) {
+        try {
+            return new ResultEntity<>(HttpStatus.OK, "校验通过", businessFeasibilityStepThreeService.validate(answer, TokenProvider.getJWTUser(request)));
+        } catch (ServiceException e) {
+            return new ResultEntity<>(e.getCode(), e.getMessage());
+        }
+    }
+
     @DeleteMapping("/{taskKey}")
     @ApiOperation("删除当前学生指定实训任务答案")
     public ResultEntity delete(@PathVariable String taskKey,
diff --git a/src/main/java/com/sztzjy/linkCommerce/entity/dto/BusinessFeasibilityStepThreeValidationRequest.java b/src/main/java/com/sztzjy/linkCommerce/entity/dto/BusinessFeasibilityStepThreeValidationRequest.java
new file mode 100644
index 0000000..fbf018c
--- /dev/null
+++ b/src/main/java/com/sztzjy/linkCommerce/entity/dto/BusinessFeasibilityStepThreeValidationRequest.java
@@ -0,0 +1,10 @@
+package com.sztzjy.linkCommerce.entity.dto;
+
+public class BusinessFeasibilityStepThreeValidationRequest {
+    private String reportUrl;
+    private String reportName;
+    public String getReportUrl() { return reportUrl; }
+    public void setReportUrl(String reportUrl) { this.reportUrl = reportUrl; }
+    public String getReportName() { return reportName; }
+    public void setReportName(String reportName) { this.reportName = reportName; }
+}
diff --git a/src/main/java/com/sztzjy/linkCommerce/entity/dto/BusinessFeasibilityStepThreeValidationResult.java b/src/main/java/com/sztzjy/linkCommerce/entity/dto/BusinessFeasibilityStepThreeValidationResult.java
new file mode 100644
index 0000000..20dbc05
--- /dev/null
+++ b/src/main/java/com/sztzjy/linkCommerce/entity/dto/BusinessFeasibilityStepThreeValidationResult.java
@@ -0,0 +1,10 @@
+package com.sztzjy.linkCommerce.entity.dto;
+
+public class BusinessFeasibilityStepThreeValidationResult {
+    private boolean valid;
+    private String message;
+    public boolean isValid() { return valid; }
+    public void setValid(boolean valid) { this.valid = valid; }
+    public String getMessage() { return message; }
+    public void setMessage(String message) { this.message = message; }
+}
diff --git a/src/main/java/com/sztzjy/linkCommerce/service/BusinessFeasibilityStepThreeService.java b/src/main/java/com/sztzjy/linkCommerce/service/BusinessFeasibilityStepThreeService.java
new file mode 100644
index 0000000..3cfc224
--- /dev/null
+++ b/src/main/java/com/sztzjy/linkCommerce/service/BusinessFeasibilityStepThreeService.java
@@ -0,0 +1,9 @@
+package com.sztzjy.linkCommerce.service;
+
+import com.sztzjy.linkCommerce.config.security.JwtUser;
+import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepThreeValidationRequest;
+import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepThreeValidationResult;
+
+public interface BusinessFeasibilityStepThreeService {
+    BusinessFeasibilityStepThreeValidationResult validate(BusinessFeasibilityStepThreeValidationRequest request, JwtUser user);
+}
diff --git a/src/main/java/com/sztzjy/linkCommerce/service/impl/BusinessFeasibilityStepThreeServiceImpl.java b/src/main/java/com/sztzjy/linkCommerce/service/impl/BusinessFeasibilityStepThreeServiceImpl.java
new file mode 100644
index 0000000..89fcc58
--- /dev/null
+++ b/src/main/java/com/sztzjy/linkCommerce/service/impl/BusinessFeasibilityStepThreeServiceImpl.java
@@ -0,0 +1,38 @@
+package com.sztzjy.linkCommerce.service.impl;
+
+import com.sztzjy.linkCommerce.config.exception.handler.ServiceException;
+import com.sztzjy.linkCommerce.config.security.JwtUser;
+import com.sztzjy.linkCommerce.entity.StudentTrainingAnswer;
+import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepThreeValidationRequest;
+import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepThreeValidationResult;
+import com.sztzjy.linkCommerce.service.BusinessFeasibilityStepThreeService;
+import com.sztzjy.linkCommerce.service.StudentTrainingAnswerService;
+import org.apache.commons.lang3.StringUtils;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Service;
+
+import java.util.Locale;
+
+@Service
+public class BusinessFeasibilityStepThreeServiceImpl implements BusinessFeasibilityStepThreeService {
+    private static final String TASK_KEY = "business-feasibility";
+    @Autowired private StudentTrainingAnswerService studentTrainingAnswerService;
+
+    @Override
+    public BusinessFeasibilityStepThreeValidationResult validate(BusinessFeasibilityStepThreeValidationRequest request, JwtUser user) {
+        if (user == null || StringUtils.isBlank(user.getUserId())) throw new ServiceException(HttpStatus.UNAUTHORIZED, "请先登录后再提交");
+        if (user.getRoleId() != 4) throw new ServiceException(HttpStatus.FORBIDDEN, "仅学生可提交实训报告");
+        StudentTrainingAnswer saved = studentTrainingAnswerService.get(TASK_KEY, null, user);
+        if (saved == null || StringUtils.isBlank(saved.getStep1Answer()) || StringUtils.isBlank(saved.getStep2Answer())) throw new ServiceException(HttpStatus.BAD_REQUEST, "请先完成并保存前两步商业可行性论证");
+        String url = request == null ? "" : StringUtils.trimToEmpty(request.getReportUrl());
+        String name = request == null ? "" : StringUtils.trimToEmpty(request.getReportName());
+        if (StringUtils.isBlank(url) || !isSupported(url, name)) throw new ServiceException(HttpStatus.BAD_REQUEST, "请上传 PDF、Word、PNG 或 JPG 格式的可行性论证报告");
+        BusinessFeasibilityStepThreeValidationResult result = new BusinessFeasibilityStepThreeValidationResult(); result.setValid(true); result.setMessage("校验通过"); return result;
+    }
+
+    private boolean isSupported(String url, String name) {
+        String value = (url + " " + name).toLowerCase(Locale.ROOT);
+        return value.matches(".*\\.(pdf|doc|docx|png|jpg|jpeg)(?:[?\\s].*)?");
+    }
+}
diff --git a/src/test/java/com/sztzjy/linkCommerce/service/impl/BusinessFeasibilityStepThreeServiceImplTest.java b/src/test/java/com/sztzjy/linkCommerce/service/impl/BusinessFeasibilityStepThreeServiceImplTest.java
new file mode 100644
index 0000000..1e448ea
--- /dev/null
+++ b/src/test/java/com/sztzjy/linkCommerce/service/impl/BusinessFeasibilityStepThreeServiceImplTest.java
@@ -0,0 +1,35 @@
+package com.sztzjy.linkCommerce.service.impl;
+
+import com.sztzjy.linkCommerce.config.exception.handler.ServiceException;
+import com.sztzjy.linkCommerce.config.security.JwtUser;
+import com.sztzjy.linkCommerce.entity.StudentTrainingAnswer;
+import com.sztzjy.linkCommerce.entity.dto.BusinessFeasibilityStepThreeValidationRequest;
+import com.sztzjy.linkCommerce.service.StudentTrainingAnswerService;
+import org.junit.jupiter.api.Test;
+import org.springframework.test.util.ReflectionTestUtils;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+class BusinessFeasibilityStepThreeServiceImplTest {
+    @Test
+    void validatesUploadedReportAfterFirstTwoSteps() {
+        BusinessFeasibilityStepThreeValidationRequest request = request("/profile/upload/feasibility-report.docx", "feasibility-report.docx");
+        assertTrue(serviceWithFirstTwoSteps().validate(request, student()).isValid());
+    }
+
+    @Test
+    void rejectsUnsupportedReportAndMissingPrerequisite() {
+        assertThrows(ServiceException.class, () -> serviceWithFirstTwoSteps().validate(request("/profile/upload/report.zip", "report.zip"), student()));
+        BusinessFeasibilityStepThreeServiceImpl service = new BusinessFeasibilityStepThreeServiceImpl(); StudentTrainingAnswerService answers = mock(StudentTrainingAnswerService.class); when(answers.get(anyString(), any(), any(JwtUser.class))).thenReturn(new StudentTrainingAnswer()); ReflectionTestUtils.setField(service, "studentTrainingAnswerService", answers);
+        assertThrows(ServiceException.class, () -> service.validate(request("/profile/upload/report.pdf", "report.pdf"), student()));
+    }
+
+    private BusinessFeasibilityStepThreeServiceImpl serviceWithFirstTwoSteps() { BusinessFeasibilityStepThreeServiceImpl service = new BusinessFeasibilityStepThreeServiceImpl(); StudentTrainingAnswerService answers = mock(StudentTrainingAnswerService.class); StudentTrainingAnswer answer = new StudentTrainingAnswer(); answer.setStep1Answer("{}"); answer.setStep2Answer("{}"); when(answers.get(anyString(), any(), any(JwtUser.class))).thenReturn(answer); ReflectionTestUtils.setField(service, "studentTrainingAnswerService", answers); return service; }
+    private BusinessFeasibilityStepThreeValidationRequest request(String url, String name) { BusinessFeasibilityStepThreeValidationRequest request = new BusinessFeasibilityStepThreeValidationRequest(); request.setReportUrl(url); request.setReportName(name); return request; }
+    private JwtUser student() { JwtUser user = new JwtUser(); user.setUserId("stu-1"); user.setRoleId(4); return user; }
+}