Abstract: The fiber laser welding was used to weld the 4 mm thick T6 state GW103K rare earth magnesium alloy plate.The influence of laser welding process parameters on the weld formation and the mechanical properties of the welded joints at room temperature and high temperature was investigated by changing the laser power, welding speed, defocusing amount and heat input. The results show that in case of single pass penetration, the above welding process parameters have an effect on the weld formation, and the weld back width is most affected by the welding process parameters. At the same time, the welding heat input also has an important influence on the structure and mechanical properties of the welded joints. With the increase of the welding heat input, the grain size of weld center, the width and the grain size of heat affected zone increase, the room temperature and high-temperature mechanical properties of the welded joint, and the microhardness of each area of the welded joint decrease. The heat affected zone is the weak part of the welded joint.