Abstract: Co-based alloy powder was used for laser cladding on the substrate (ER9 wheel material)without preheating and preheating at 200 ℃, respectively.By optical microscope(OM), scanning electron microscope(SEM), energy spectrometer(EDS), X-ray diffraction (XRD)and Vickers hardness tester, the influence rule of preheating on the structure, element/phase composition and hardness changes of the cladding layer was studied.The results show that the structure of the cladding layer after the substrate with and without preheating is mainly composed of γ-Co and Cr₂₃C₆ phases, but the preheating of the substrate can increase the intensity of γ-Co diffraction peaks.The preheating of the substrate can obtain a crack-free cladding layer, but the grain size increases.The average hardness of the cladding layer after the substrate without and with preheating is 464.2 HV and 329.82 HV, respectively, which are higher than the hardness of the substrate(293.2HV).