Abstract: A way of representing the relationship of different features in a part termed Undirected Feature Dependency Graph（UFDG） is proposed．Base on this approach，the similarity of process plan instances of different parts can be evaluated by the subgraph isomorphism method，after that，a filter function is performed to scale down the instance set，then the user can select instance from it to start his process plan design．This approach has the advantages of catholicity and fine resolving performance．