In order to study the effect of different SiCp content on the microstructure and properties of AZ91Dalloy，the effects of SiCp on the as-cast microstructure and mechanical properties of AZ91D magnesium alloy wereinvestigated by means of metallographic microscope，scanning electron microscopy and X-ray diffraction analysis.The average grain size and area of the composites were determined. The results show that，in this experiment，thehigher the content of SiCp，the smaller the size of the crystal grains. Adding proper amount of SiCp can improve themicrostructure of AZ91D magnesium alloy and improve its mechanical properties. In this experiment，when theSiCp content is 0. 5%，the grain refining effect of the AZ91D magnesium alloy Is most obvious，and the grain size is103. 05 μm. The addition of SiCp can also improve the tensile strength，elongation and hardness of AZ91Dmagnesium alloy. The tensile strength，elongation and hardness of the alloy are 218. 34 MPa，6. 17% and78. 42 HV.