Abstract: In order to study the effect of micro-arc oxidation (MAO)time on the growth regularity of ceramic coating of aluminum alloy for piston, ZL109 aluminum alloy was treated by MAO for different time.The effects of oxidation time on the surface morphology, surface roughness, surface porosity, coating thickness, growth rate and phase composition of the coating were investigated by roughness meter, SEM, XRD and Image J software. The results show that the surface roughness and thickness of the coating increase with the increase of oxidation time, and “volcano deposit” characteristic is also more obvious. However, the porosity and growth rate first increase and then decrease with increasing oxidation time. The surface porosity of the coating is the largest, when the oxidation time is 20 min, which is 20.2%. During the period of 10 min to 20 min, the growth rate is the largest, which is 2.1 μm/min. Meanwhile, the content of γ-Al₂O₃ and α-Al₂O₃ in the coating also increase gradually with the increase of oxidation time.