The invention relates to a drive axle dynamic characteristic computing method considering input torque changing. The method comprises the steps that (1) a drive axle global coordinate system is defined; (2) a shafting beam unit model is established; (3) a nonlinear roller bearing model is established; (4) a gear model is established; (5) a connecting part model is established; (6) a shell finite element model and a dimension-reducing model are established; (7) a complete drive axle system dynamics model is established; (8) bearing stiffness under different input torque working conditions is computed; and (9) the drive axle system dynamic characteristics under different input torque working conditions are computed. According to the method, a finite element method and a modality comprehensive method are used for establishing the complete drive axle system dynamics model which comprises a main speed reducing assembly, a differential mechanism assembly, a hub assembly, a shell and the like, and the dynamic characteristics of a drive axle system can be computed accurately and efficiently.