The key technologies of CAD/CAM integration of mechanical parts which include parametric modeling technology, model transformation of CAD/CAE and finite element modeling were studied. Based on redevelopment of UG, the process of parametric modeling about typical part was achieved. The identification, selection, extraction, and removal of the details in the CAD model were analyzed. The extraction approach of the mid-surface in the dimensional reduction of the CAD model was executed. The CAD/CAE integration system of the design and finite element analysis for mechanical parts was established by the redevelopment of UG and ANSYS with Visual C++, UG/Open and APDL as tools. The parametric design and automatic finite element analysis for mechanical parts were implemented.