The residual stress of the S355 J2 W steel MAG welded joint was measured and analyzed by X-ray diffraction method and ultrasonic critical refraction longitudinal wave method. The results show that:the X-ray diffraction method and ultrasonic critical refraction longitudinal wave method can be used for S355 J2 W steel MAG welded joint residual stress measurement. The residual stress value of the ultrasonic method is 30 ,4,0 MPa larger than that of the X-ray method in the weld and heat affected zone. The distribution of residual stress in each test area is similar,and the residual tensile stress is larger in the weld and heat affected zone,and the base metal which is away from the center of the weld is residual compressive stress. The residual stress peak of the central area of is greater than the starting arc region and the ending arc region.