Abstract: 316 stainless steel welding experiments were carried out with a low power pulsed laser welding machine. Based on the surface morphology, microstructure, microhardness and energy dispersive spectrum (EDS), the effect of defocusing amount on the weld structure and hot cracking was analyzed. The results show that with the increase of defocusing amount, the weld microstructure is gradually refined and compact, and the tendency of hot cracking decreases gradually. With the increase of defocusing amount, the weld penetration and weld width reduce, but the width to depth ratio increases. When the width to depth ratio is greater than 7.5, the welding hot cracking completely disappears. Adjusting the defocusing amount changes the distribution of laser energy, which leads to the segregation of S, P and other elements to the surface during solidification. So the defocusing amount can effectively control the welding hot cracking of 316 stainless steel.