Fiber laser welding and metal-inert gas (MIG) welding of SUS301L-HT sheets with 2 mm thickness are carried out, and differences in welding formation, microstructure and mechanical properties between two types of joints are researched and compared. Welding formation of two types joints is different from each other, and formation of laser welding joint is better than that of MIG welding joint. Stable and uniform welding formation is acquired in fiber laser welding process and almost no angular distortion is found in laser welding joint and width of beads and heat affected zone (HAZ) is narrow. Microstructure of laser welding joints is quite different from that of MIG welding joint. Microstructure of laser welding bead consists of fine columnar austenitic dendritic crystals and interdendritic δ ferrite, and size of grain grows a little in HAZ; phase composition of MIG welding bead contains massive austenitic and a little δ ferrite, and microstructure in HAZ gets different obviously as distance from fusion line changes. Mechanical properties of two types joints are different. Tensile property of laser welding joint is much better than that of MIG welding joint. Tensile sample of laser welding joint breaks at bead, in tensile experiment, in a classical ductile way, ductility of the joint is up to 48.2%, and tensile strength is up to 979.1 MPa.