Abstract: Laser cladding was used to prepare Al-Si coating on AZ91D magnesium alloy by using Al-Si eutectic alloy powders. Microstructure of the coatings was analyzed by optical microscope, scanning electronic microscope, energy dispersive spectroscopy and X-ray diffractometer. The phase constitution, composition and transformation in the coating were analyzed with Thermo-Calc software. The results showed that the coating was divided into two layers. In the upper layer, Mg₂Si dendrites and fine needle-like Al₃Mg₂ are uniformly distributed on Al₁₂Mg₁₇ matrix and its crystallization process is liquid→liquid+Mg₂Si→ Mg₂Si+Al₁₂Mg₁₇→Mg₂Si+Al₁₂Mg₁₇+Al₃Mg₂. The bottom layer consists of Mg₂Si particles, α-Mg dendrites and(α-Mg+A₁₂M₁₇) eutectics and its crystallization process is liquid→liquid+Mg₂Si→liquid+Mg₂Si+α-Mg→Mg₂Si+α-Mg+(α-Mg+A₁₂M₁₇) eutectics. The calculated results are well consistent with the experimental data and it is beneficial to understanding the microstructure evolution of laser claded Al-Si coating on AZ91D magnesium alloy.