With the certain deposition process, the conversion coatings by four different pretreatments on LF21 were studied. The morphology and the chemical composition of the conversion coatings were examined by scanning electron microscopy (SEM). The corrosion resistance was investigated by electrochemical impedance spectroscopy (EIS) and the salt spray test. The results showed that the different pretreatments had obvious effect on the cerium conversion coatings. For the certain deposition process, the optimal pretreatment process was identified.