Abstract: The aluminum alloy profile welded structure is used in the high-speed train body. With the train starting and braking, rendezvous and docking and entering and leaving the tunnel, the stress of the car body is complicated, and the fatigue failure phenomenon is more prominent. The residual stress has a great influence on the fatigue strength of the aluminum alloy body. In this paper, based on the theory of acoustic elasticity, the application of ultrasonic residual stress testing technology in aluminum alloy car body structural parts is studied by means of test, so as to achieve non-destructive, rapid and accurate testing. By testing the residual stress of the newly manufactured car body, the internal stress state of the car body structure is monitored; through comparing the residual stress distribution law of the state of large parts and the state of the whole vehicle, the residual stress change law during the assembly process is studied. It has important practical value and significance for the reliability assessment of the whole life cycle of the key parts of the car body.