Abstract: Al and Si powders codeposition on the HP40 steel surface was conducted by applying direct current field (DCF).The microstructure,coating thickness and phase composition of the complex coating were investigated by means of optical microscope and X-ray diffraction.The high temperature oxidation resistance and the corrosion resistance were studied as well.The results show that the thickness of the Al and Si complex coating increased with the increase of current intensity,holding time and heating temperature under the DCF,while both the high temperature oxidation resistance and the corrosion resistance decreased.The phase of the Al-Si complex coating was mainly composed of AlFe and AlN.