<p>The dynamic performance of the ball screws significantly affects the positioning accuracy of the machine tools, which is mainly related to the ball-groove contact characteristics, and previous studies have ignored the effect of the sudden changes in the number of loaded balls due to the ball recirculation process. To solve this problem, this paper proposes an eight DOF dynamic model of the ball screws that includes the ball recirculation process and screw shaft’s deformation, which captures the transient impacts during the transition section when the balls enter and exit. Firstly, the geometric relationship between the ball and groove centers is determined based on rigid body kinematics and coordinate transformation matrix, and the ball-groove contact loads in the working and transition sections are derived. Then, a nonlinear dynamic model of the ball screws is established by simplifying it to a mass-spring-damping structure, and the correctness of the proposed model is verified by comparing it with the experimental results. Finally, the dynamic characteristics of the ball screws under the effects of the ball recirculation process are investigated.</p>