diff --git a/api.py b/api.py
index a0151db..323088c 100644
--- a/api.py
+++ b/api.py
@@ -60,8 +60,10 @@ def verify_token(authorization: str | None = Header(default=None)) -> str:
 
 
 def _check_owner(rec: dict, username: str) -> None:
-    """文件归属校验: admin 可操作全部, 普通用户只能操作自己的"""
+    """文件归属校验: 每个账户只操作自己的空间 (admin 只认 admin/无主旧文件)"""
     if username == "admin":
+        if rec.get("user_id") not in ("admin", None):
+            raise HTTPException(status_code=403, detail="无权访问他人文件")
         return
     if rec.get("user_id") != username:
         raise HTTPException(status_code=403, detail="无权访问他人文件")
diff --git a/db.py b/db.py
index eadfbac..58e32db 100644
--- a/db.py
+++ b/db.py
@@ -258,12 +258,13 @@ class ServerDB:
         return dict(row) if row else None
 
     def list_files(self, user_id: str) -> list[dict[str, Any]]:
-        """文件记录 (ls 端点): admin 看全部, 普通用户看自己的"""
+        """文件记录 (ls 端点): 每个账户只看自己的空间 (admin 含无主旧文件)"""
         with self._conn() as conn:
             if user_id == "admin":
                 rows = conn.execute(
                     "SELECT file_id, file_name, size, sha256, created_at FROM files "
-                    "ORDER BY created_at DESC"
+                    "WHERE user_id = ? OR user_id IS NULL ORDER BY created_at DESC",
+                    ("admin",),
                 ).fetchall()
             else:
                 rows = conn.execute(
@@ -280,10 +281,13 @@ class ServerDB:
             return cur.rowcount > 0
 
     def sum_files_size(self, user_id: str) -> int:
-        """文件 size 总和 (配额统计用): admin 全部, 普通用户自己的"""
+        """文件 size 总和 (配额统计用): 每个账户只算自己的空间"""
         with self._conn() as conn:
             if user_id == "admin":
-                row = conn.execute("SELECT COALESCE(SUM(size), 0) FROM files").fetchone()
+                row = conn.execute(
+                    "SELECT COALESCE(SUM(size), 0) FROM files WHERE user_id = ? OR user_id IS NULL",
+                    ("admin",),
+                ).fetchone()
             else:
                 row = conn.execute(
                     "SELECT COALESCE(SUM(size), 0) FROM files WHERE user_id = ?",
diff --git a/tests/test_api.py b/tests/test_api.py
index 860b241..3751537 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -388,6 +388,11 @@ class AccountTest(unittest.TestCase):
         # alice 自己可以下载/删除
         r = self.client.get(f"/api/files/{file_id}/chunk/1", headers=auth_a)
         self.assertEqual(r.status_code, 200)
-        # admin (SZ_TOKEN) 可见全部
+        # admin (SZ_TOKEN) 也只看自己的空间, 看不到 alice 的文件
         r = self.client.get("/api/files", headers=AUTH)
-        self.assertTrue(any(f["file_id"] == file_id for f in r.json()["files"]))
+        self.assertTrue(all(f["file_id"] != file_id for f in r.json()["files"]))
+        # admin 下载/删除 alice 的文件 -> 403
+        r = self.client.get(f"/api/files/{file_id}/chunk/1", headers=AUTH)
+        self.assertEqual(r.status_code, 403)
+        r = self.client.delete(f"/api/files/{file_id}", headers=AUTH)
+        self.assertEqual(r.status_code, 403)