Abstract: The numerical models of temperature field and thermal stress field of laser cladding Al-Si eutectic powder on WE43 magnesium alloy surface were established by using Gaussian surface heat source. By varying the laser melting power and laser scanning velocity, the temperature clouds maps were obtained, and the temperature thermal cycling curves and thermal strain distribution maps of the same node were also obtained. The results indicate that the highest temperature and thermal stress of the laser clad coating both rise continuously with the increase of laser power. In addition, when the laser power is kept constant 600 W, the highest temperature of the laser clad coating exhibits a decreasing trend with the increase of the laser scanning velocity, however, the thermal stresses display a first decreasing and then increasing trend. Theoretically, the optimal laser power for laser coating of Al-Si eutectic powder on the surface of WE43 magnesium alloy is 600 W and the optimal scanning velocity is 3 mm/s.