A　large　area　of　Co-based　alloy　coatings　on　alloy　struction　steel　20CrMo　has　been　successfully　obtained　by　using　a　6　kW　CO2　laser　and　synchronous　powder　feeding　system.　By　means　of　metalloscopy　and　X-ray　diffraction,　the　microstructure　of　the　coating　is　investigated.　The　microhardness,　bending　strength　and　corrosion　resistance　are　measured.　The　experimental　results　show　that　the　cladding　layer　is　of　fine　dendritic　microstructure.　The　phases　of　coating　are　composed　of　Co-based　solid　solution,　CrB,　M23C6　et　al.　Compared　with　cemented　carbide　hot　roller　presently,　the　cladding　layer　has　a　little　higher　microhardness　equivalent　bending　strength　and　improved　corrosion　resistance.