The purpose of this research is to clarify the mechanism of the instantaneous vehicle lateral acceleration. We have led the outbreak factor of the vehicle lateral acceleration, by studying the rotation center of rigid body and the turning center of the center of gravity. The cause of vehicle lateral acceleration is explained clearly, and the dynamic behavior can be shown by a diagram. Applying this study to J-turn simulation, we have shown a vehicle trace as a body slip angle and a vehicle motion state in a diagram.