Abstract: Ball screw pair is an important part of NC machine tool mechanical transmission. Because of the continuous change of cutting parameters, the axial load has dynamic time-varying characteristics, and the decline of precision, preload force, and friction moment shows time-varying characteristics. Based on the time-varying force model, the time-varying force model, the time-varying wear model, the time-varying pre-tightening force and the friction moment decay model of the ball screw pair under the time-varying axial force condition were deduced by the elastic Hertz theory. Compared with the theoretical model, the wear depth of ball screw under the condition of sequential axial force loading and constant axial force loading was compared with that of the theoretical model. The validity and rationality of the decay model of time-varying axial force loading performance of ball screw pair were verified. The research is of great significance to improving the precision and retention of precision ball screw pair.