Abstract: Large motor shafts have large diameters and complex processing procedures,and the final products are prone to flexural deformation,which affects the assembly accuracy and stability of the working state.In order to track and analyze the characteristics of residual stress changes before and after different processes,this paper adopts the ultrasonic method to non-destructively monitor the residual stresses in the three states of the same 35CrMo motor shaft's spindle billet,rib plate welding and post-weld annealing,and analyze and evaluate the test results.The test results show that:the stress at the machined step of the spindle blank is higher,and there is a high stress point at the forging clamping,and the symmetric measurement line stress distribution trend is similar;the spindle in the post-weld annealing state,the welded fascia plate around the more significant compressive stress,the fascia plate welding caused by the weld toe of the pressure near the tensile stress,the distance from the I end of the farther region of the compressive stress,the welding generated compressive stress and tensile stress.The interaction between the compressive and tensile stresses generated by welding aggravates the overall flexural deformation of the shaft.