In this paper, the laser welding process of 1 mm-thickness 316L stainless steel sheet was studied, and the effect of laser welding parameters on the penetration was analyzed by orthogonal experiment. The results show that with the increase of laser power, the penetration increases correspondingly; with the increase of welding speed, the penetration decreases correspondingly, and the penetration is almost inversely proportional to the welding speed. When the welding speed is greater than 0.03 m/s, the penetration decreases significantly; when the forward defocusing is adopted, the penetration decreases with the increase of defocusing. When the defocusing is greater than 8 mm, the penetration decreases obviously; when Ar, He and N2 are used as protective gases, the penetration is arranged in the order of He>N2>Ar; metallographic analysis results show that when the power is greater than 1 600 W, the penetration of welds reaches more than 1 mm. The best welding parameters are as follows: power is 1 800 W, welding speed is 0.026 m/s, defocusing is 7 mm, shielding gas argon and gas flow is 10 L/min.