The butt welding of SUS301L-MT stainless steels is conducted by means of the metal active gas arc welding (MAG), laser welding and laser-MAG hybrid welding, respectively, and the effects of these three different welding processes on the microstructure and mechanical properties of joints are investigated and compared. The results show that, the welded joints obtained under these three different welding processes are all duplex-phase structures with δ-ferrite and austenite. The width of the heat affected zone of MAG welded joints has a size of 3 mm, while both that of the laser welding and laser-MAG welded joints are only 1 mm. All the residual stress peaks under three welding processes distribute at weld toe, and the MAG welded joints have the highest longitudinal and transverse residual stress peak values. The laser-MAG welded joints show the highest tensile strength with a value of 906 MPa.