Abstract: The ball screw feed system is a key component of CNC machine tool. The motion precision of the ball screw feed system is closely related with the dynamic characteristics, and has an important influence on the machining accuracy of CNC machine tool. The dynamic characteristics of the ball screw feed system have obvious time-varying characteristics. In order to explore the influence of the mass and placement of the workpiece on the dynamic characteristics of the ball screw feed system, a dynamic model of the ball screw feed system was constructed based on the lumped mass method, and the accuracy of the model was verified by the finite element method. Based on the constructed dynamic model, the influence of the mass and placement of the workpiece on the dynamic characteristics of the ball screw feed system was analyzed, and its response surface was constructed. The results showed that the natural frequency of the ball screw feed system decreased with the increase of the quality of the workpiece. The closer the workpiece is to the center of gravity of the worktable, the less influence it has on the natural frequency of the system. The results can be used to guide the placement of the workpiece on the worktable in the actual machining process.