The fiber laser welding is used to weld the T6 state Mg-10 Gd-3 Y-0.5 Zr plate for creating welding procedure window. The welding parameters are optimized by orthogonal experimental design method with the high temperature tensile strength of welded joints as the evaluation index. The optimal welding parameters are achieved by range analysis and variance analysis,and the degree of influence of each welding parameter and optimum welding procedure are determined. The effect of laser power on the high temperature mechanical properties of the welded joint is studied. The high temperature mechanical properties and high temperature tensile fracture morphology of welded joints under the optimal welding parameters are analyzed.The result shows that the laser power has the most significant influence on the high temperature mechanical properties of the welded joint. Under the optimal welding parameters,the average tensile strength of the welded joint at 200 ℃ is 281.1 MPa,which is 86.3% of the base metal,and the elongation is 7.4%,which is 65.4% of the base metal. And the joint is well formed,the grain size in the weld metal zone is small,and the fracture mode of the base metal and the joint both are ductile fracture.