The organic-inorganic hybrid sol was prepared using an alkaline silica sol modified by acid-catalyzed hydrolytic polycondensation of methyltrimethoxysilane (MTMS) in a water-bath condition of 60oC, and then the water-based primer and topcoat were prepared through adding the pigments and nano-TiO2 suspension respectively. Through spraying and baking, the organicinorganic composite coating on the treated aluminum alloy was obtained. The optimum range of P/B (weight ratio of the pigment/binder) is determined between 1:1 and 1.5:1 by investigating the influence of the P/B of the primer on the adhesion and impact resistance of the coating. The microstructure of the coating was characterized by optical microscopy and scanning electron microscopy. The results show that there are lots of holes and lamellar structure in the primer coating and the obtained topcoat coating is uniform, smooth and dense. The coating of ~30 μm in thickness is mainly composed of three elements of silicon, aluminum and titanium, in which transition layer of ~10 μm is included. The physicochemical properties suggest that the coatings on aluminum alloy can meet the needs of finishing coating very well.