Abstract: Single factor experimental design was used for M6 welded square nuts and SAPH370 pickled hot-rolled steel plates in order to optimize the nut welded joint quality. The electrode force, welding current and welding time were picked out as the process parameters and the Pull-out load were weighted into a welding quality index. The mathematical model between the welding quality index and process parameters was obtained by regression analysis. The research results show that the welding current has the greatest effect on the Pull-out load, and the welding time and electrode pressure have a small effect on the Pull-out load. When the electrode pressure is small, the welding time has a large effect on the Pull-out load. When the electrode pressure is large, the welding current has a large effect on the Pull-out load. The interaction effect between electrode pressure and welding current is the largest, the interaction effect between welding current and welding time and the interaction effect between electrode pressure and welding time are smaller.