Abstract: In order to research residual stress for non-penetration laser lap welding of stainless steel plate, the 2 mm+2 mm cold rolling SUS301L stainless steel plates were welded by axial flow CO2laser. The indentation strain-gage method, sectioning-relaxation strain-gage method and X-ray diffraction method were used to measure residual stress in the lap welded joints. The results from the indentation strain-gage method show that the peak value of longitudinal residual stress is 237 MPa, the maximum transverse residual stress is 124 MPa, and all the residual stress values reflect an average around 2 mm near the surface layer. The results from the sectioning-relaxation method show that the peak value of longitudinal residual stress is 155 MPa, the transverse residual stress is 55 MPa, and all the residual stresses are an average in the sample whole section with 5 mm×5 mm×2 mm. The results from X-ray diffraction method show that the maximum longitudinal residual stress value is 344 MPa, the transverse residual stress peak value is 163 MPa, and all the residual stresses are an average in the circle of 1～2 mm in diameter near the surface layer. Comparatively speaking, the error from X-ray method is higher than the other methods due to the obvious texture and coarse grains.