A Mechanical model of impact and contact between the ball and re-circulating mechanism in ball screw was brought forward according to the Hertz contact model and classical impact theory, along with the joint relationship of re-circulating mechanism and nut taken into account. Then the formula of the impact force and contact time was induced, which the elastic coefficient of restitution was considering in contact time calculation. Moreover, a special test unit was designed for contact time measurement and the contact time was measured. The result indicates that the new model proposed in this paper is closer to the practical situation than the old model proposed in literature. Based on works mentioned above, the influence of impact angle, parameters of structure and material on impact force was analyzed by numerical simulation.