diff --git a/backend/app/services/oa_related_approval.py b/backend/app/services/oa_related_approval.py
new file mode 100644
index 00000000..6b73f38c
--- /dev/null
+++ b/backend/app/services/oa_related_approval.py
@@ -0,0 +1,114 @@
+"""关联审批单：字段扁平化与 form_data 抽链"""
+from __future__ import annotations
+
+from typing import Any, Dict, List, Optional, Sequence, Tuple
+
+LAYOUT_SKIP = frozenset(
+    {"fcRow", "fcTable", "col", "row", "elCard", "space", "divider", "html", "title", "text", "tag"}
+)
+UPLOAD_TYPES = frozenset({"upload", "fcUpload", "image", "oaAttachment"})
+LONG_TYPES = frozenset({"textarea", "input"})
+
+
+def _walk_rules(rules: Any, out: List[dict]) -> None:
+    if not isinstance(rules, list):
+        return
+    for r in rules:
+        if not isinstance(r, dict):
+            continue
+        out.append(r)
+        children = r.get("children") or (r.get("props") or {}).get("rule") or []
+        if isinstance(children, list):
+            _walk_rules(children, out)
+
+
+def _schema_rules(schema: Any) -> List[dict]:
+    if isinstance(schema, list):
+        out: List[dict] = []
+        _walk_rules(schema, out)
+        return out
+    if not isinstance(schema, dict):
+        return []
+    out = []
+    _walk_rules(schema.get("rule") or schema.get("rules") or [], out)
+    return out
+
+
+def _format_value(typ: str, raw: Any) -> Tuple[str, bool]:
+    """returns (text, fullWidth)"""
+    if typ in UPLOAD_TYPES:
+        if raw is None or raw == "" or raw == []:
+            n = 0
+        elif isinstance(raw, list):
+            n = len(raw)
+        else:
+            n = len([x for x in str(raw).split(",") if x.strip()])
+        return f"{n} 个", False
+    if typ == "relatedApproval":
+        if isinstance(raw, list):
+            n = len([x for x in raw if str(x).strip()])
+        elif raw:
+            n = 1
+        else:
+            n = 0
+        return f"已关联 {n} 条", False
+    if isinstance(raw, list):
+        text = "、".join(str(x) for x in raw if x is not None and str(x) != "")
+    elif isinstance(raw, dict):
+        text = str(raw.get("label") or raw.get("value") or raw)
+    else:
+        text = "" if raw is None else str(raw)
+    full = typ in LONG_TYPES and len(text) > 40
+    return text, full
+
+
+def flatten_form_fields_for_summary(schema: Any, form_data: Optional[Dict[str, Any]]) -> List[Dict[str, Any]]:
+    data = form_data or {}
+    out: List[Dict[str, Any]] = []
+    for rule in _schema_rules(schema):
+        typ = str(rule.get("type") or "")
+        if not typ or typ in LAYOUT_SKIP:
+            continue
+        field = str(rule.get("field") or "").strip()
+        if not field:
+            continue
+        label = str(rule.get("title") or rule.get("label") or field)
+        text, full = _format_value(typ, data.get(field))
+        item: Dict[str, Any] = {"label": label, "value": text}
+        if full:
+            item["fullWidth"] = True
+        out.append(item)
+    return out
+
+
+def extract_related_approval_links(
+    schema: Any, form_data: Optional[Dict[str, Any]]
+) -> List[Tuple[str, str]]:
+    """Ordered unique (field_key, to_instance_id)."""
+    data = form_data or {}
+    seen = set()
+    links: List[Tuple[str, str]] = []
+    for rule in _schema_rules(schema):
+        if str(rule.get("type") or "") != "relatedApproval":
+            continue
+        field = str(rule.get("field") or "").strip()
+        if not field:
+            continue
+        raw = data.get(field)
+        ids: Sequence[Any]
+        if isinstance(raw, list):
+            ids = raw
+        elif raw is None or raw == "":
+            ids = []
+        else:
+            ids = [raw]
+        for x in ids:
+            tid = str(x or "").strip()
+            if not tid:
+                continue
+            key = (field, tid)
+            if key in seen:
+                continue
+            seen.add(key)
+            links.append((field, tid))
+    return links
diff --git a/backend/tests/test_oa_related_approval.py b/backend/tests/test_oa_related_approval.py
new file mode 100644
index 00000000..36ff5ff9
--- /dev/null
+++ b/backend/tests/test_oa_related_approval.py
@@ -0,0 +1,50 @@
+import unittest
+
+from app.services.oa_related_approval import (
+    extract_related_approval_links,
+    flatten_form_fields_for_summary,
+)
+
+
+class TestFlatten(unittest.TestCase):
+    def test_skips_layout_and_summarizes_upload(self):
+        schema = {
+            "rule": [
+                {"type": "html", "title": "说明"},
+                {"type": "input", "field": "reason", "title": "事由"},
+                {"type": "upload", "field": "files", "title": "附件"},
+                {"type": "relatedApproval", "field": "prev", "title": "关联"},
+                {"type": "textarea", "field": "long", "title": "详细说明"},
+            ]
+        }
+        data = {
+            "reason": "出差",
+            "files": ["a.png", "b.png"],
+            "prev": ["id1", "id2"],
+            "long": "很长很长的说明文字" * 5,
+        }
+        fields = flatten_form_fields_for_summary(schema, data)
+        labels = [f["label"] for f in fields]
+        self.assertNotIn("说明", labels)
+        self.assertEqual(fields[0], {"label": "事由", "value": "出差"})
+        self.assertEqual(fields[1]["value"], "2 个")
+        self.assertEqual(fields[2]["value"], "已关联 2 条")
+        self.assertTrue(fields[3].get("fullWidth"))
+
+    def test_extract_links_with_field_key_and_dedupe(self):
+        schema = {
+            "rule": [
+                {"type": "relatedApproval", "field": "relA"},
+                {
+                    "type": "fcRow",
+                    "children": [{"type": "relatedApproval", "field": "relB"}],
+                },
+            ]
+        }
+        data = {"relA": ["x", "x", ""], "relB": "solo"}
+        links = extract_related_approval_links(schema, data)
+        self.assertEqual(links, [("relA", "x"), ("relB", "solo")])
+
+
+if __name__ == "__main__":
+    unittest.main()