Considering the electromechanical coupling characteristics of a ball screw feed system into account, the system structure is subdivided to several fine parts. By reducing the complexity and coupling degree of feed system, a block-lumped modeling method for the screw feed system is proposed. Based on the dynamic theory, the dynamic model of the ball screw feed system was established by using the instantaneous variation method, and the ball screw system was processed by the multi-degree-of-freedom (DOF) flexible system. The bending, torsion and axial deformation were also taken into account. The coupling effect of the flexible bodies and the bending deformation of the screw shaft were analyzed and deduced, which was different from the coupling effect between the vibration of the concentrated mass model (or mixed model) of the ball screw feed system and equations. Finally, the validity of the established dynamic model is verified by the vibration experiment and principal component analysis (PCA), which provides the study basis for the dynamic analysis of the screw feed drive system.