In this paper, ceramic coatings prepared on 2024 Al alloy surface in electrolyte by micro-arc oxidation are studied. The parameter of discharge and rate of ceramic coating formation are investigated. We analyzed microstructure and phase composition of the coatings by scanning electronic microscopy (SEM) and X-ray diffraction (XRD), and studied the tribological performance of the coatings. The reactions on the electrode surface are deduced and the mechanism of coating formation has been analyzed. The results show that the relation between the thickness and reaction time is not linear. The ceramic coatings contain phase γ-Al2O3 andα-Al2O3; there is a big difference in contents of phase composition between inner coating and outer coating due to the different cooling rates of them. In MAO process, the coating undergoes a course of melting, solidifying and cooling. The coating can be divided into three layers, namely, transition layer, compact layer, and loose layer. The coating and substrate adheres firmly by a metallurgical process. Not only the elements of electrolyte (K, Si) and substrate (Cu) are found in the coatings but also the element of cathode (Fe). The Si-Al-O complex compound is formed in the discharge channels under high energy density condition.