For dynamic process planning under reconfigurable manufacturing system (RMS), the method of process planning based on similarity theory was presented. Part feature description was built as well as case index structure. Procedure combination principia suited for reconfigurable machine tool (RMT) and sort rule based on relation among features were given. Similarity process information was created by comparability judgment of part feature multiple-tree, procedure was combined by the agglomerative hierarchical clustering method, and every working-step was sorted in procedure group. Moreover, the process planning system was developed with Visual C++ and verified through example test.