The purpose of this study is to clarify mechanism of the balance during the golf swing. In the golf swing, inertial and centrifugal force are applied to the player's body. In such case, golf player carry out weight shift to keep balance. At first, we conduct dynamic analysis of the swing using the model of double pendulum likened arm and club and model of human trunk, to calculate the trajectory of the center of pressure. We carry out experiment to measure the trajectory of center of pressure during golf swing by using the force plate. Next, the effect of the weight shift on the trajectory of examined by using a simple mathematical model of the human body. Through the discussion, it can be seen that the acceleration pattern of the human trunk influence on the center of pressure significantly.