Abstract: Ball screw drive system (BSDS) plays a crucial role in determining the precision of machine tools. The dynamic positioning accuracy of BSDS is closely related to the dynamic characteristics. However, the dynamic characteristics of BSDS are time-varying and are affected by the structure, friction, load and cutting force. It is very important to describe accurately the time-varying vibration characteristics of BSDS for its precision research. To analyze the influence of time-varying dynamic characteristics on dynamic positioning accuracy of the system, this paper presents a time-variant elastodynamic model that can depict the dynamic behavior of a slender ball screw drive system (SBSDS) within the whole stroke. Furthermore, model-based the time-varying dynamic characteristics of SBSDS are analyzed through natural frequencies. Then, the harmonic response of the ball screw drive system within the whole stroke is simulated to analyze the vibration mode of the system. The vibration characteristics of the system vary within the whole stroke when the worktable moves at 10 m/min, compared with being immobile at 2 m/min. Moreover, the change law is consistent with the change law of dynamic characteristics within the whole stroke. So, it is considerable that the nonlinear varying for improving the positioning accuracy of SBSDS. Experiments were conducted on a SBSDS from a five-axis machine tool. The results show that the tracking error is mainly determined by the acceleration, and its fluctuation amplitude and fluctuation characteristics are related to the velocity and the position of the workbench. The dynamic positioning error of the SBSDS is dominated by the system elastic deformation at the acceleration stage, while it is determined by the combination of elastic deformation and vibration characteristics of the system at the constant-rate period.