A large area of Co based alloy coatings on alloy struction steel 20CrMo has been successfully obtained by using a 6 kW CO 2 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,M 23 C 6 et al.. Compared with cemented carbide hot roller presently, the cladding layer has a little higher microhardness, equivalent bending strength and improved corrosion resistance.