Abstract: High-cycle fatigue tests of 15-5PH welding parts were carried out at the stress ratios of 0.1, 0.5 and −1. S-N curves and fatigue strength at the different stress ratios were obtained by data analysis. The results show that the fatigue life of 15-5PH welding parts decreases linearly with the increase of stress level, and the fatigue strength of the welding part is the largest when the stress ratio is 0.5, the second when the stress ratio is 0.1, and the smallest when the stress ratio is −1. Fractures analysis results indicate that the fatigue cracks initiated at the crossing corner between the base and the residual height at the welding back, with a line source and steps at the source, and the fracture surfaces present cleavage and fatigue striations characteristics. Fish scale grains can be seen on the surface of the residual height of the weld, and the fish scale grains solidify to form groove marks of different depths. The crack originates from groove marks. The fatigue lives of the parts are mainly influenced by the radius of the crossing corner and the residual height.