The anti-corrosion of the conversion coating which is formed by La( NO₃)₃ ·6 H₂O was evaluated with polarization curve, and also compared the chromium phosphate film and non-rare phosphate conversion coating. Adhesion force between the conversion coatings and the organic coating were studied through crossing grid method and immersing corrosion test .The results showed that the transmission resistance of conversion coating with rare earth additive was increased by comparing with non-rare phosphate conversion coating; The anti-corrosion of the conversion coating was increased noticeably. But comparing with chromium phosphting, in the weak polarized scope, both of the corrosion resistances were close. Adhesion force between the conversion coating with rare earth as additive and the organic coating was obviously superior to that of chromate phosphate process.