diff --git a/api/tests/unit_tests/models/test_dataset_models.py b/api/tests/unit_tests/models/test_dataset_models.py
index 51d95c4239..3f14ebe8bf 100644
--- a/api/tests/unit_tests/models/test_dataset_models.py
+++ b/api/tests/unit_tests/models/test_dataset_models.py
@@ -12,7 +12,9 @@ This test suite covers:
 import json
 import pickle
 from datetime import UTC, datetime
+from types import SimpleNamespace
 from unittest.mock import Mock, patch
+from urllib.parse import parse_qs, urlparse
 from uuid import uuid4
 
 from core.rag.index_processor.constant.index_type import IndexTechniqueType
@@ -676,6 +678,51 @@ class TestDocumentSegmentIndexing:
         # Assert
         assert segment.hit_count == 5
 
+    def test_document_segment_attachments_prefers_files_url_for_source_url(self, monkeypatch):
+        """Test attachment source URLs use FILES_URL before falling back to CONSOLE_API_URL."""
+        # Arrange
+        segment = DocumentSegment(
+            tenant_id="tenant-1",
+            dataset_id="dataset-1",
+            document_id="document-1",
+            position=1,
+            content="Test",
+            word_count=1,
+            tokens=2,
+            created_by="user-1",
+        )
+        segment.id = "segment-1"
+        attachment = SimpleNamespace(
+            id="upload-1",
+            name="image.png",
+            size=128,
+            extension="png",
+            mime_type="image/png",
+        )
+
+        monkeypatch.setattr("models.dataset.time.time", lambda: 1700000000)
+        monkeypatch.setattr("models.dataset.os.urandom", lambda _: b"\x01" * 16)
+        monkeypatch.setattr("models.dataset.dify_config.SECRET_KEY", "unit-secret")
+        monkeypatch.setattr("models.dataset.dify_config.FILES_URL", "https://files.example.com")
+        monkeypatch.setattr("models.dataset.dify_config.CONSOLE_API_URL", "https://console.example.com")
+
+        with patch("models.dataset.db") as mock_db:
+            mock_db.session.execute.return_value.all.return_value = [(Mock(), attachment)]
+
+            # Act
+            attachments = segment.attachments
+
+        # Assert
+        assert len(attachments) == 1
+        source_url = attachments[0]["source_url"]
+        parsed = urlparse(source_url)
+        query = parse_qs(parsed.query)
+        assert parsed.netloc == "files.example.com"
+        assert parsed.path == "/files/upload-1/image-preview"
+        assert query["timestamp"] == ["1700000000"]
+        assert query["nonce"] == ["01010101010101010101010101010101"]
+        assert query["sign"][0]
+
     def test_document_segment_error_tracking(self):
         """Test document segment error tracking."""
         # Arrange