1wt% SiC nanoparticles reinforced Mg-9Al-1Zn magnesium matrix composite was fabricated by stir casting and hot extrusion. Effect of stirring for 10min and 30min respectively on microstructure and mechanical properties of SiCp/Mg-9Al-1Zn nanocomposite was researched. The results show that the grains of the matrix in the as-cast SiCp/Mg-9Al-1Zn nanocomposite stirring for 30min are mainly refined. But the mechanical properties of nanocomposite decline due to the increase of agglomerated SiC nanoparticles and Mg17Al12 phases with network morphology along the grain boundaries. After hot extrusion, a bimodal microstructure composed of alternate arrays of fine DRXed grains and relatively coarse DRXed grains is formed. Particularly, for as-extrusion nanocomposites stirring for 30min, the fine DRXed region can be increased and the distribution of SiC nanoparticles is more homogenous, which can exhibit superior mechanical properties compared with as-extruded SiCp/Mg-9Al-1Zn nanocomposite stirring for 10min.