diff --git a/src/main/java/com/sztzjy/linkCommerce/service/impl/MarketOpportunitySelectionStepFiveServiceImpl.java b/src/main/java/com/sztzjy/linkCommerce/service/impl/MarketOpportunitySelectionStepFiveServiceImpl.java
index ca6ba10..fa36cec 100644
--- a/src/main/java/com/sztzjy/linkCommerce/service/impl/MarketOpportunitySelectionStepFiveServiceImpl.java
+++ b/src/main/java/com/sztzjy/linkCommerce/service/impl/MarketOpportunitySelectionStepFiveServiceImpl.java
@@ -54,7 +54,12 @@ public class MarketOpportunitySelectionStepFiveServiceImpl implements MarketOppo
 
     @SuppressWarnings("unchecked")
     private void requireCompletedStepFour(String answerJson) {
-        Map<String, Object> outcome = JSON.parseObject(answerJson, LinkedHashMap.class);
+        Map<String, Object> outcome;
+        try {
+            outcome = JSON.parseObject(answerJson, LinkedHashMap.class);
+        } catch (RuntimeException error) {
+            throw badRequest("请先完成并保存第 4 步数据可视化");
+        }
         Object rawVisualization = outcome == null ? null : outcome.get("visualization");
         Object url = rawVisualization instanceof Map ? ((Map<String, Object>) rawVisualization).get("url") : null;
         if (!(rawVisualization instanceof Map) || url == null || StringUtils.isBlank(String.valueOf(url))) throw badRequest("请先完成并保存第 4 步数据可视化");
diff --git a/src/test/java/com/sztzjy/linkCommerce/service/impl/MarketOpportunitySelectionStepFiveServiceImplTest.java b/src/test/java/com/sztzjy/linkCommerce/service/impl/MarketOpportunitySelectionStepFiveServiceImplTest.java
new file mode 100644
index 0000000..9452899
--- /dev/null
+++ b/src/test/java/com/sztzjy/linkCommerce/service/impl/MarketOpportunitySelectionStepFiveServiceImplTest.java
@@ -0,0 +1,36 @@
+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.MarketOpportunitySelectionStepFiveValidationRequest;
+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.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+class MarketOpportunitySelectionStepFiveServiceImplTest {
+    @Test
+    void validateRejectsMalformedSavedStepFourAnswerAsBadRequest() {
+        MarketOpportunitySelectionStepFiveServiceImpl service = new MarketOpportunitySelectionStepFiveServiceImpl();
+        StudentTrainingAnswerService answers = mock(StudentTrainingAnswerService.class);
+        StudentTrainingAnswer answer = new StudentTrainingAnswer();
+        answer.setStep4Answer("{not-valid-json");
+        when(answers.get(anyString(), any(), any(JwtUser.class))).thenReturn(answer);
+        ReflectionTestUtils.setField(service, "studentTrainingAnswerService", answers);
+
+        assertThrows(ServiceException.class, () -> service.validate(new MarketOpportunitySelectionStepFiveValidationRequest(), student()));
+    }
+
+    private JwtUser student() {
+        JwtUser user = new JwtUser();
+        user.setUserId("stu-1");
+        user.setRoleId(4);
+        return user;
+    }
+}