In Section 1, we describe process of ball-bat collision using kinetic model, and derive the post-collision ball speed as a function of the hitting location. Then we differentiate the function and find out where the sweet spot is. The result successfully explains the best location is not at the end of the bat in consistent with our practical experience. In Section 2, based on the model in Section 1, we add two assumptions, supposing corking only influences mass and moment of inertia of bat. Then the maximum outgoing ball speed is only depended on mass of bat. The result shows properly corking will enhance the bat performance. In Section 3, we explain “trampoline effect” in dynamic model and throw light on energy transformation in collision process. We conclude that COR is related to materials, and aluminum bats perform better than wood bats.