diff --git a/src/evidence.ts b/src/evidence.ts
new file mode 100644
index 0000000..cc0edc3
--- /dev/null
+++ b/src/evidence.ts
@@ -0,0 +1,9 @@
+import type { CaseResult } from './model';
+
+export function evidenceState(result: CaseResult, reviewDate: string): string | null {
+  if (result.status === 'not-run') return '未执行';
+  if (result.status === 'failed') return '验证失败';
+  if (!/^\d{4}-\d{2}-\d{2}$/.test(result.evidenceUntil)) return '证据日期无效';
+  if (result.evidenceUntil < reviewDate) return '证据过期';
+  return null;
+}