Intermetallic compounds layer will be formed at the interfaces between alloy layer and matrix in the diffusion process of hot dip aluminized steel, which is beneficial to enhance the binding ability of alloy layer with matrix. However, when the thickness of intermetallic compounds exceeds the certain value, the vast extending force of interfacial void will cause the crack of intermetallic compounds and greatly weaken the spall resistance of aluminized layer. Therefore it is very important for the applications of hot dip aluminized steel to research and control the formation of intermetallic compounds at the interfaces. According to the characteristics of diffusion process of hot dip aluminized steel, the growing model of intermetallic compounds were established in the paper. The computed results were in accord with the experimental value. It can provide reference to the choice of the diffusion parameters of hot dip aluminized steel.