The influence of silicon addition on the microstructure and properties of corundum-mullite refractory was studied. Results show that Si addition as raw material of the matrix can accelerate mullite crystal formation. The oxidation of Si leads to nucleation of mullite via liquid phase and gas phase. The network microstructure is formed by tiny mullite crystals with few glass phase. So it enhances obviously the high temperature strength of sintered corundum-mullite refractory.