The ball screw drive system is obtained widespread application in the modern machine. Along with the improving of feeding velocity and working precision, its dynamic analysis becomes more and more important. Considering the bearing stiffness and the contact deformation between the worktable and the screw, the drive screw is seen as a bar under elastic supports at both ends and with an internal moving elastic support. Using boundary conditions and matching conditions, the longitudinal vibration frequency equation of the screw is derived and the mode shape of the screw is solved. The vibration frequency is analyzed when the worktable moves from the left to the right end of the screw. The effect of the system parameters on the natural frequency and the mode shape are studied to supply a base for designing the drive system.