Abstract: The ultrasonic system of accurately measuring internal stress of welding structure is established based on acoustoelasticity effect and critically refracted longitudinal wave that is most sensitive to stress in order to shorten the time of the welding residual stress measurement.A new series decreasing residual stress methods,such as trailing rotating extrusion,trailing impactive rolling,electromagnetic impact and pre-stress,are verified by this measurement system.The experiment results show that the decreasing degree of residual stress can validate the effectiveness of technical parameters by those methods.The measurement speed of the nondestructive system is quicker than that of traditional section release methods,which accelerates the research process.