Abstract: The fiber laser welding is used to weld the T6 state Mg-10Gd-3Y-0.5Zr plate. Taking the high temperature tensile strength as the reference index. The process parameters were optimized by orthogonal test, and the influence of laser power on the high temperature mechanical properties of the joint was analyzed. The paper use SEM, XRD and HRTEM to observe and analyze the joint weld center structure, heat affected zone structure and high temperature tensile fracture. The results show that the laser power has the most significant effect on the high temperature mechanical properties of the welded joint. Under the optimal process parameters, the average high-temperature tensile strength of the welded joint is 292.1 MPa at 200 ℃, which is 84.5% of the base material. The elongation is 8.6%, which is up to 71.1% of the base material at 200 ℃. The change of laser power will affect the grain size, heat-affected width and phase composition of the weld, which will affect the high-temperature mechanical properties of the joint. The fracture modes of the welded joint and the base metal are ductile fractures at 200 ℃.The heat-affected zone is the weak part of the joint.