By optimizing the welding parameters of nonpenetration laser lap welding of stainless steel with two plate thickness combinations（2 mm +1.5 mm, 1.5 mm +2 mm）, the laser welding quality control under the condition of multi-parameter coupling was realized, and their fatigue performances were studied. The welding process test is designed by orthogonal test method. According to the orthogonal test results, the relationship between three key welding parameters（power,welding speed, defocusing amount） and shear strength of welded joints of these two plate thicknesses combinations is ana lyzed. And the optimal welding parameters are obtained, namely1.5 mm+2 mm plate thickness combination（power of 3 700 W,welding speed of 4 330 mm/min, defocusing amount of +4 mm）and 2 mm+1.5 mm plate thickness combination（power of 3 700 W, welding speed of 4 580 mm/min, defocusing amount of0 mm）. The fatigue properties of laser welded joints of these two plate thickness combinations under the optimal welding parameters are comparatively analyzed. The fatigue strength of welded joint of 2 mm+1.5 mm composite is higher than that of1.5 mm +2 mm composite, which provides a reference for further parameters optimization r and fatigue properties study of laser welding of stainless steel carbody.