Abstract: Co-Cr based alloy Stellite12 powder was used for multilayer laser cladding on 304L stainless steel substrate alveolar groove. The microstructure and phase composition of Stellite12 cladding layer were studied by optical microscope（OM）, scanning electron microscope（SEM）, energy spectrometer（EDS）, X-ray diffraction（XRD） and Vickers microhardness tester. The mechanism of crack formation and propagation of cladding layer was investigated. The crack was analyzed by means of stress-induced crack combined with XRD phase analysis, EDS element analysis and the microstructure observation,and the microhardness characterization was carried out for the area around the crack. The results show that cracks are caused by the tensile stress and restraint stress of the coating. The crack presents intergranular or transgranular fracture along eutectic carbide, which is brittle crack. The average microhardness around the crack area region is 450-540 HV.