diff --git a/core/management/commands/seed_data.py b/core/management/commands/seed_data.py
index 240a69d..47df3c3 100644
--- a/core/management/commands/seed_data.py
+++ b/core/management/commands/seed_data.py
@@ -19,6 +19,19 @@ from core.models import (
 class Command(BaseCommand):
     help = "Seed database with user-confirmed initial content"
 
+    def add_arguments(self, parser):
+        parser.add_argument(
+            "--clear",
+            action="store_true",
+            help="Delete existing content pages before seeding",
+        )
+
+    def _clear_existing(self):
+        for model in [ArticlePage, SkeletonProjectPage, ProjectIndexPage,
+                      ScenarioPage, ScenarioIndexPage, ArticleIndexPage]:
+            model.objects.all().delete()
+        self.stdout.write("  Cleared existing content pages")
+
     def _create_snippets(self):
         languages = [
             ("Python", "python"),
@@ -50,6 +63,13 @@ class Command(BaseCommand):
     def _create_pages(self):
         home = HomePage.objects.get(slug="home")
 
+        if ScenarioIndexPage.objects.filter(slug="scenarios").exists():
+            scenario_index = ScenarioIndexPage.objects.get(slug="scenarios")
+            project_index = ProjectIndexPage.objects.get(slug="projects")
+            article_index = ArticleIndexPage.objects.get(slug="articles")
+            self.stdout.write("  Page tree already exists, skipping")
+            return scenario_index, project_index, article_index
+
         scenario_index = ScenarioIndexPage(title="Scenarios", slug="scenarios")
         home.add_child(instance=scenario_index)
 
@@ -68,7 +88,7 @@ class Command(BaseCommand):
         article_index = ArticleIndexPage(title="Articles", slug="articles")
         home.add_child(instance=article_index)
 
-        self.stdout.write("  Page tree created")
+        self.stdout.write("  Page tree ready")
         return scenario_index, project_index, article_index
 
     def _get_snippets(self):
@@ -226,6 +246,10 @@ class Command(BaseCommand):
         ]
 
         for proj in projects:
+            if SkeletonProjectPage.objects.filter(slug=proj["slug"]).exists():
+                self.stdout.write(f"    Skipping existing project: {proj['title']}")
+                continue
+
             scenarios = proj.pop("scenarios")
             languages = proj.pop("languages")
             frameworks = proj.pop("frameworks")
@@ -239,6 +263,7 @@ class Command(BaseCommand):
                 project.frameworks.add(*frameworks)
             if databases:
                 project.databases.add(*databases)
+            project.save()
             self.stdout.write(f"    Created project: {proj['title']}")
 
     def _create_articles(self, article_index):
@@ -297,13 +322,25 @@ class Command(BaseCommand):
         ]
 
         for art in articles:
+            if ArticlePage.objects.filter(slug=art["slug"]).exists():
+                self.stdout.write(f"    Skipping existing article: {art['title']}")
+                continue
+
             related = art.pop("related_projects")
             article = ArticlePage(**art)
             article_index.add_child(instance=article)
             article.related_projects.add(*related)
+            article.save()
             self.stdout.write(f"    Created article: {art['title']}")
 
     def handle(self, *args, **options):
+        if options["clear"]:
+            self._clear_existing()
+
+        if not options["clear"] and ScenarioIndexPage.objects.filter(slug="scenarios").exists():
+            self.stdout.write("Seed data already exists. Use --clear to reset.")
+            return
+
         self.stdout.write("Creating snippets...")
         self._create_snippets()
 
@@ -320,6 +357,19 @@ class Command(BaseCommand):
         # Verify
         self.stdout.write("")
         self.stdout.write("=== Seed verification ===")
+        for proj in SkeletonProjectPage.objects.all():
+            sc = proj.scenarios.count()
+            la = proj.languages.count()
+            status = "OK" if sc >= 1 and la >= 1 else "MISSING_M2M"
+            self.stdout.write(
+                f"  {proj.title}: scenarios={sc}, languages={la} [{status}]"
+            )
+        for art in ArticlePage.objects.all():
+            rp = art.related_projects.count()
+            status = "OK" if rp >= 1 else "MISSING_M2M"
+            self.stdout.write(
+                f"  {art.title}: related_projects={rp} [{status}]"
+            )
         self.stdout.write(
             f"Scenarios: {ScenarioPage.objects.count()} "
             f"(≥3: {ScenarioPage.objects.count() >= 3})"
diff --git a/core/tests.py b/core/tests.py
index 7df0f4e..6adde42 100644
--- a/core/tests.py
+++ b/core/tests.py
@@ -161,6 +161,16 @@ class SkeletonProjectPageTests(PageTreeMixin, TestCase):
         except ValidationError:
             self.fail("full_clean() should pass with all M2M set")
 
+    def test_m2m_persists_after_save_and_reload(self):
+        project = self._make_project()
+        project.languages.add(self.lang)
+        project.scenarios.add(self.scenario)
+        project.save()
+
+        reloaded = SkeletonProjectPage.objects.get(pk=project.pk)
+        self.assertGreaterEqual(reloaded.scenarios.count(), 1)
+        self.assertGreaterEqual(reloaded.languages.count(), 1)
+
 
 class ArticlePageTests(PageTreeMixin, TestCase):
     @classmethod
diff --git a/progress.md b/progress.md
index 17c8a8f..ad01929 100644
--- a/progress.md
+++ b/progress.md
@@ -246,3 +246,16 @@
 - 阻塞：无。
 - 下一步：T-201 实现基础页面框架（Phase 2 前台 MVP）。
 
+## 2026-07-06 T-104 seed_data M2M 持久化修复
+
+- 状态：DONE
+- 变更：
+  - `core/management/commands/seed_data.py`：`add_child()` 后 M2M `.add()` 仅在内存操作 cluster，不持久化到 DB；新增 `project.save()` / `article.save()` 确保关联写入
+  - 添加 `--clear` 参数和重复运行保护
+  - `core/tests.py`：新增 `test_m2m_persists_after_save_and_reload` 测试——save() 后从 DB 重新加载，断言 `scenarios.count() >= 1` 和 `languages.count() >= 1`
+- 验证：
+  - `manage.py seed_data --clear`：5 个项目全部 `scenarios≥1, languages≥1 [OK]`，2 篇文章全部 `related_projects=1 [OK]`
+  - `manage.py test core home`：21 tests passed（新增 1 个持久化测试）
+- 阻塞：无。
+- 下一步：T-201 实现基础页面框架（Phase 2 前台 MVP）。
+