The purpose of this study is to analyze the stress effect of the shaft, the head speed of the golf club, and the reaction force of the arm as well as the wrist under the process of the down swing. By using two softwares, the researcher conducted the study. First, I-DEAS software was used to model the club head with shaft. Next, Dyna3D software was used to analyze the swinging condition. After that the golf club and ball were placed in the three dimensional space and analyzed the dynamic behavior with the field of gravity. In order to simulate the action of swing of the golf club, the driving moment was input to the arm and the wrist. Through changing the thickness of the shaft, three different flexibility and weight of the shaft was specified. Later on, the researcher discussed the swing effect of differently flexible shaft and weight of the shaft. From the result of analysis, stiff shaft resulted in stable swing but lower head speed under the same driving moment. By contrast, the soft shaft generated higher head speed and dynamic loft angle but it resulted in less stable club head traveling path. Besides, the stiff shaft generated higher resultant force and moment to the arm and the wrist under the same driving moment. It is believed that this study will provide some reliable computer simulation data for the reference in golf sport.