A S-N curve for predicting the life of welding joints is proposed to accurately predict the fatigue life of SUS304 stainless steel spot welded joints on construction machinery. According to several common structural forms of spot welding joints, tension shear fatigue samples with different plate thickness combinations were prepared, and the fatigue life data of the samples were obtained through fatigue test. The accurate nugget diameter is obtained by CT scanning experiment, then the finite element model of the specimen is established, and the accuracy of the model is verified by optical strain measurement experiment. Then, based on Rupp equivalent structural stress method and fatigue test data, S-N curves integrating different plate thickness combinations and load ratios are established, and Goodman correction method is used to eliminate the influence of load ratio. Finally, the finite element model of vibrating conveyor is established, the transient dynamic analysis is carried out to obtain the structural stress of vibrating groove solder joint, whose life is predicted based on the established S-N curve. The results show that there is no fatigue problem in each solder joint of the vibration groove but solder joint redundancy, so it can be designed lightweight.