Abstract: The crack initiation and propagation mechanism of SiC/AZ91D magnesium matrix composites with different shapes and volume fractions of SiC particles under uniaxial compression was investigated by using the finite element analysis software Abaqus to introduce a cohesive force element into the interface of the finite element model. The introduction of cohesive force element avoids the defects of prefabrication crack and singularity of crack tip in linear elasticity, and provides a new method to solve the problem of crack propagation. The results show that the compressive strengths of circular, original shape and square SiC/AZ91D magnesium matrix composites are 474.853 MPa, 435.783 MPa and 397.211 MPa, respectively. The time of crack initiation and fracture are 15.6 μs, 14.4 μs, 12.6 μs, 22.2 μs, 20.4 μs, 18 μs after loading, respectively. The crack propagation mechanism of circular particle composites is the crack propagation initiated by matrix damage, which leads to material fracture, while the crack propagation mechanism of square and original shape particle composites is the crack initiation at the junction of particle and matrix, and the primary crack and secondary crack are connected with each other, which lead to material fracture. The crack initiation and fracture time of SiC/AZ91D magnesium matrix composites with 10vol%, 15vol% and 20vol% original shape particles are 15.6 μs, 14.4 μs, 11.4 μs, 22.2 μs, 20.4 μs and 18 μs after loading, respectively. The crack propagation process of SiC/AZ91D magnesium matrix composites is accelerated with the increase of particle volume fraction.