The methods of underlying welding including laser welding and laser-MIG hybrid welding in combination with methods of filling welding including laser-MIG hybrid welding and MIG welding(melt inert-gas welding),are used to complete the welding of 15-mm-thick 316L austenitic stainless steel. The microstructure and mechanical properties of the weld joints in each group were studied. The results show that the weld joint obtained by all laser-MIG hybrid welding has the best formation. There is cellular structure in the center of laser-MIG hybrid welding layer, while the MIG welding layer is almost all columnar crystal structure. The tensile strength of the filling layer welded by hybrid welding is higher than that welded by MIG, while the strength of the underlying layer welded by laser is comparable to that welded by hybrid welding, and all fractures are ductile fractures. The micro-hardness of the weld center of the two different underlying layers is higher than that of the base metal, the micro-hardness of the weld center of the hybrid welding filling layer is slightly higher than that of the base metal, and the micro-hardness of MIG filling layer is lower than that of the base metal.