In this experiment Al2O3 gradient ceramics coating is cladded on the high Cr cast steel by 5kW crosscurrent CO2 laser with Ni-based alloy which is used as transitive metal. The microstructure is analyzed with optics microstructure analyzer and the crystal grain characteristic is studied. The microstructure of the laser cladding layer have the plane crystal zone, the butcher crystal zone, the dendrite zone and the surface equiaxed grain zone that grow along the substrate. The microstructure of the coating compared with the substrate is extremely tiny, and the microstructure of the multi-layer cladding presents stratification. The phase composition of the clad coating is composed primarily of NiAl intermetallic compound, but also includes γ-FeNi and a little Ni3Al compound. In the coating the Al2O3 pellet that some present the unit crystal form, and some little accumulate in together, plays the dissemination strengthening role in the coating material. The massive twin crystals and the dislocation staffing are presented in the clad coating.