diff --git a/CHANGELOG.md b/CHANGELOG.md
index 679a6202..0deca53f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # Changelog
 
 ## Unreleased
+- [BE] ⚡ **DBML 대규모 컬럼 위치 계산 O(N)화**: relation별 증분 카운터로 `column_position`을 계산해 growing-list 재순회를 제거하고, 1,000개 컬럼과 다중 relation의 연속 위치를 회귀 테스트로 검증합니다.
 - [BE] 🔒 **공유 export 전 경로 redaction**: 공개 share의 SQL / index-design / reversing-spec export에서 코멘트·`example_value`를 제거합니다. 단위 테스트로 누출을 차단합니다.
 - [BE] 🛠️ **함수 인덱스 중복 오탐 수정**: `lower(email)` 등 expression index를 평문 컬럼 인덱스의 중복으로 잘못 판단하지 않도록 괄호 파서를 강화했습니다.
 - [Docs] README를 상용 기준 기능 설명으로 갱신 (MVP skeleton 표현 제거, share redaction·diff/export 반영).
diff --git a/backend/app/spec/dbml_import.py b/backend/app/spec/dbml_import.py
index b93454a9..f4016cb1 100644
--- a/backend/app/spec/dbml_import.py
+++ b/backend/app/spec/dbml_import.py
@@ -136,6 +136,8 @@ def parse_dbml(text: str) -> dict[str, Any]:
     in_ignored_block = 0
     in_indexes = False
 
+    col_counts_by_oid: dict[int, int] = {}
+
     for raw_line in text.splitlines():
         # ReDoS guard: no legitimate DBML line approaches this length; capping
         # input size per regex call bounds worst-case backtracking to O(1).
@@ -207,11 +209,13 @@ def parse_dbml(text: str) -> dict[str, Any]:
         settings = (cm.group("settings") or "").lower()
         oid = oid_by_table[current]
         is_pk = bool(re.search(r"\bpk\b|primary\s+key", settings))
+        pos = col_counts_by_oid.get(oid, 0) + 1
+        col_counts_by_oid[oid] = pos
         columns.append(
             {
                 "relation_oid": oid,
                 "column_name": col_name,
-                "column_position": sum(1 for c in columns if c["relation_oid"] == oid) + 1,
+                "column_position": pos,
                 "data_type": cm.group("type"),
                 "is_not_null": is_pk or "not null" in settings,
                 "has_default": "default:" in settings,
diff --git a/backend/tests/test_dbml_import.py b/backend/tests/test_dbml_import.py
index 2c034bef..e76a43bb 100644
--- a/backend/tests/test_dbml_import.py
+++ b/backend/tests/test_dbml_import.py
@@ -110,3 +110,33 @@ def test_pathological_table_header_dots_are_rejected_fast():
     assert {(r["schema_name"], r["relation_name"]) for r in snap["relations"]} == {
         ("public", "users")
     }
+def test_column_positions_scale_and_reset_per_relation() -> None:
+    first_columns = "\n".join(f"  column_{index} integer" for index in range(1_000))
+    text = f"""
+Table wide_relation {{
+{first_columns}
+}}
+Table second_relation {{
+  first_column integer
+  second_column integer
+}}
+"""
+
+    snapshot = parse_dbml(text)
+    relation_oids = {
+        relation["relation_name"]: relation["relation_oid"]
+        for relation in snapshot["relations"]
+    }
+    wide_positions = [
+        column["column_position"]
+        for column in snapshot["columns"]
+        if column["relation_oid"] == relation_oids["wide_relation"]
+    ]
+    second_positions = [
+        column["column_position"]
+        for column in snapshot["columns"]
+        if column["relation_oid"] == relation_oids["second_relation"]
+    ]
+
+    assert wide_positions == list(range(1, 1_001))
+    assert second_positions == [1, 2]