This paper describes a structural design tool for punches and dies in 3D progressive dies of motor core based on association design technology. Based on the classification and 3D modeling method of punches and dies, the associated model is set up to describe the holes on plates of die set for punches and dies. The proposed tool integrates the design knowledge of progressive dies for motor core to automate the design for punches, dies and corresponding holes on plates. This design tool is constructed on a PC and integrated with SolidWorks software. We use progressive die for the motor core with rotator, stator and vice-stator as a concrete example to demonstrate the power of the design tool. The results show that it can not only improve design quality but also save both time and costs dramatically.