The invention discloses a method for growing a blue ceramic layer in situ on the surface of aluminum alloy. The method includes the steps that the surface of an aluminum alloy workpiece to be treatedis ground and polished on silicon carbide sandpaper and is cleaned and dried to obtain the pre-treated aluminum alloy workpiece; and the pre-treated aluminum alloy workpiece is placed in an electrolyte solution, 2 to 5 g/L of cobalt hydroxide is added into the electrolyte solution, then micro-arc oxidation treatment is carried out, and thus a uniform blue micro-arc oxidized ceramic layer is prepared on the surface of the aluminum alloy workpiece. According to the method for growing the blue ceramic layer in situ on the surface of the aluminum alloy, the blue ceramic layer has the good thickness and good binding force with a substrate, color retention is good, and the film performance effect is quite ideal.