The density and anodic potentiodynamic polarization (PDP) in different diluted acidic sulphate solution of the aluminum electrodeposion coating on Q235 steel substrate, obtained in the molten salt of AlCl3,NaCl and KCl and treated by diffusion treatment, have been investigated. The results indicated that with the increase of temperature of diffusion treatment, the dencity of the coatings increases first, then reduces little. At 500°C, the dencity is biggest, 2.76g/cm3, which is almost equal to that of compact pure aluminum. As-received coating displays a current oscillation behavior on the anodic potentiodynamic polarization curves in different diluted acidic sulphate solution . And with the increase of diffusion temperature, the current oscillation behaviors donated by the current oscillation domains in solution of 180g/L H2SO4 gradually disappeared. When the temperature is up to 500°C and 700°C, no current oscillation phenomena can be observed. Based on these phenomena, a mode between the porosity of the coating, which was affected by the temperature of diffusion treatment, and current oscillation behaviors was roughly established.