The solution mainly containing Zn2+, Mn2+, Ni2+ and H2PO4- was used to prepare phosphate film on AZ31 magnesium alloys. The process was adjusted to the following parameters, PH value 3～4, temperature 25～40°C, treatment time 3～10 min. Surface characteristics and microstructure of the phosphate film were also investigated by SEM and XRD. The film can fit for organic coatings prepared with electrophoresis and painting.It is found that the coatings adhered well to the phosphate film, and the anti-corrosion abilities were improved. The coating has no change in 3% NaCl solution for 360h and in neutral salt fog for 168h, respectively.