The paper presents a model for CAPP(computer aided process planning)sys-tem.which integrates process data together in an open structure．The model consists of two components．The first is to construct improved class hierarchy．According to industry classification standards，process sources are abstracted and generated to form reusable and derivable classes that describe process source by inheritance，or through schema evolution．The second is to build communications among form feature，process device and process method．The model draws an expression(F，M，S)，which depicts element'S reference to another or action on others．By which，operation result is feedback in a twinkle in process planning．To practice the model in CAPP system，both OODB and KDB are used．OODB stores dynamic data that include general process source．KDBs describe mapping rules among feature，device and method．