Abstract: Process sequence planning is the main task of computer aided process planning (CAPP).Taking the rotational parts as an example,an approach of case based process sequence planning by merging together the feature technology,case-based reasoning and expert system approaches is presented.Formulas are constructed to calculate the similarity coefficients of a new part with respect to the sample cases.Strategies and algorithms are worked out to retrieve and match the most promising candidate cases and carry out the necessary modification of the relevant process sequences.The detailed matching information between the new parts and the cases are carefully recorded witch makes the case searching and modification easy to realize.The method has been successfully used in an applied CAPP system for rotational parts.