In order to improve the surface properties of the aluminum alloy, an amorphous composite coating was prepared on the surface of the aluminum alloy substrate by electrothermal explosion spraying with fully amorphous Fe-Si-B ribbons. The microstructure, phase structure and micro-hardness of the coating were characterized by SEM, XRD and Vickers hardness tester. The results show that the composite coating is composed of amorphous phase and nanocrystal phase. The coating has dense structure and low porosity. It has not been seen rough laminar microstructure that is frequently obtained by other thermal spray techniques. The amorphous composite coatings with different thickness present higher hardness and show good mechanical properties.