By single factor experiment, the best sealing prosess was obtained after studying the influence of the concentration of sodium silicate, the additives, sealing time and sealing temperature on the the sealing effect of phosphate coating. The sealing effect of silicate and chromate salt was compared by the accelerated corrosion experiment method and electrochemical test technology and the mechanism of sealing was explored. The results show that after sealing by sodium silicate, the phosphate coating has not seen the corrosion after 24 hours’neutral salt spray test and corrosion potential moves positively while the corrosion current reduces significantly; The sodium silicatesealing can improve the corrosion resistance of the phosphate coating because of the silicate deposite which can seal the hollow of the phosphate coating.