［Objective］To develop a high-performance，environmentally friendly，and mild reaction surface treatment process for aluminum alloy before electrophoretic coating，［Methods］ Organic acids were used to replace strong acids in traditional anodizing processes，and nickel free passivators with molybdate，earth cerium salts，and silane coupling agents were used for subsequent passivation processes，resulting in an anodizing+nickel free passivation process. The influence of someparameters in anodizing process and nickel free passivation process on the obtained conversion film wasinvestigated，a scanning electron microscope（SEM-EDS）with an energy dispersive spectrometer wasused to characterize the surface microstructure and element distribution of the sample after anodizing+nickel free passivation，and tested the electrophoretic paint film performance after three surface treatments：phosphating，anodizing，anodizing+nickel free passivation.［Results］When energized for 40 min with a voltage of less than 12 V and a temperature below 46 ℃，an oxide film with a thickness less than 20 micrometers could be obtained using a modified anodic oxidation process. A uniform，jet-black passivation film could be achieved by treating the surface with a nickel-free passivant containing 1. 35 g/L of earth cerium salts at a temperature range of 80 to 85 ℃ . The physical properties andcorrosion resistance of the electrophoretic paint film after anodizing and anodizing+nickel freepassivation treatment were better than those after phosphating treatment. In this study，the raw materials used for anodizing solution and nickel free passivating agent were easily available and low-cost.［Conclusion］The preparation route of anodizing film and nickel free passivating film was simple， environmentally friendly，and indicated good corrosion resistance.