In order to obtain the optimal process parameters of 304L/316 dissimilar steel sheet laser welding, the joint morphology, geometric deformation, and tensile mechanical properties were studied by using the grey correlation analysis method and Taguchi L9 orthogonal test scheme with laser power, scanning speed, and defocusing amount as the main influencing factors. The results show that the angular deformation of laser welded sheet decreases with the increase of defocusing amount. The bending deformation increases with the increase of laser power. The tensile strength increases first and then decreases with the increase of defocusing amount. When the laser power is 1500 W, the scanning speed is 15 mm/s, and the defocusing amount is + 2 mm, the tensile strength of the 304L/316 dissimilar steel welded sheet is the strongest and the deformation is the smallest, and the joint strength is higher than that of the base metal. After melting, the filler powder penetrates along the butt gap to the bottom of the sheet, forming a metal filler joint containing fine columnar crystals and a small amount of equiaxed crystals. Finally, the filler powder and the base metal form an effective metallurgical combination.