In this paper,0.6 mm stainless steel sheet and 8 mm carbon steel thick plate are used for overlapping MAG arc spot welding test. The test results of MAG spot welding parameters and equivalent nugget diameter of overlapping surface are analyzed. It is proposed that the nugget equivalent diameter of overlap surface which is larger than the requirement of product drawings and stable in size can be formed by using welding parameters in the "core" range. Suggestions on practical application of MAG arc spot welding process for stainless steel sheet lapping are put forward.