Stir casting was employed to fabricate three kinds of magnesium matrix composites, which is 5μm10vol%Grp/AZ91、(5μm5vol%Grp+5μm5vol%SiCp)/AZ91 and (5μm5vol%Grp+10μm5vol%SiCp)/AZ91 respectively. Subsequently the composites was subjected to hot extrusion at 300℃ with ram speed of 0.03mm/s. And the effect of SiCp on microstructures、mechanical properties and wear resistance was studied. The results showed that the grain size of composites increase and the phenomenon of fragmentation of graphite among the three composites became more remarkable along with the adding and increasing size of SiCp. Extruded 5μm10vol%Grp/AZ91 composite possesses poor tensile strength、hardness and plasticity which was all improved after mixing 5μm SiCp, and the mechanical properties was further enhanced by increasing the SiCp size from 5μm to 10μm. And the wear rate of 5μm10vol%Grp/AZ91 composite was decreased along with the adding and elevated size of SiCp. On the contrary, the friction coefficient was significantly increased by enlarging the SiCp size. The dominant wear mechanisms of 5μm10vol%Grp/AZ91 composite was delamination wear which totally turn into abrasive wear in 10μmSiCp hybrid reinforced composites by increasing the size of SiCp.