The invention relates to an aluminum alloy which comprises an aluminum alloy matrix and a micro-arc oxide ceramic membrane formed on the surface of the matrix, wherein the ceramic membrane comprises a bottom transition layer, a middle compact layer and a surface compact layer. The preparation method of the aluminum alloy, which is used for forming the micro-arc oxide ceramic membrane without a loose layer on the surface of the aluminum alloy, comprises the following steps: putting the aluminum alloy matrix in an oxidation tank containing electrolyte; carrying out initial oxidation treatment for the aluminum alloy matrix by adopting constant current; and continuously applying oxidation treatment to the aluminum alloy matrix by adopting positive and negative bidirectional pulse voltage, wherein positive and negative voltage keeps constant after rising to the maximum value, wherein the maximum constant positive voltage is 450V-650V, the maximum constant negative voltage is 30V-200V, the width of positive and negative pulse is 1000-10000mus, the pulse interval is 300-2000mus, the continuous oxidation treatment time is 30-180min, and the treatment temperature is between 20 DEG C and 50DEG C.