The work aims to improve the corrosion resistance of magnesium alloy by preparing rare earth cerate conversion coating on magnesium alloy. The rare earth cerate conversion coating was obtained the surface of magnesium alloy by virtue of chemical conversion technology. Effects of cerate concentration, additive content, conversion time and conversion temperature on coating morphology, composition and corrosion resistance of the conversion coating were studied by scanning electron microscopy (SEM), energy dispersion analyzer of X-ray (EDAX) and electrochemical test. The golden yellow cerium conversion coating consisted of Mg, Ce and O elements and microcracks were present on the surface. The corrosion resistance of coating firstly increased and then decreased with the increase of cerium salt and additive concentration, conversion time and temperature. The cerium conversion coating is composed of hydroxides and oxides of Mg and Ce elements. Optimum process conditions are as follows: Ce(NO3)3 mass concentration of 10~15 g/L, H2O2 additive content of 25~50 mL/L, conversion temperature of 40 ℃ and conversion time of 30 min. After chemical conversion treatment of cerium nitrate, the corrosion resistance of magnesium alloy is greatly improved.