In this study, SiCp/AZ91 composite was subjected to multi-pass equal channel angular pressing (ECAP) and high-reduction rolling (HRR). The microstructure evolution and mechanical properties of the composite were investigated. Results showed that after ECAP processing, the microstructure of composite was fully refined, and the SiC particles were highly dispersed in the matrix alloy. The ultimate strength and ductility of the ECAPed composite were obviously improved, but the yield strength was still insufficient. After the combined processing of ECAP and HRR, partial dynamic recrystallization occurred in the matrix alloy due to the non-uniform deformation caused by SiC particle disturbance and large reduction rolling, and the particle phase and precipitated phase hindered the grain growth, forming a large number of fine crystals. Heterogenous grain structure with high content of fine grains and tiny β-Al₁₂Mg₁₇ phases was formed in the composite. The yield tensile strength and tensile strength of the composite were significantly increased, and the ductility was also increased slightly, contributing to a synergistic improvement of strength and ductility.