The microstructure characteristics of the laser-clad oxide ceramic coating based on the mixture of A12O3 powder and ground enamel frit containing Co and Ni was investigated. The formed coating consists of the Fe-Si-O thin layer clinged to the carbon steel substrate, the large-sized equiaxial grain layer in the middle and the outer small-sized dendrite layer. The formation mechanism of the microstructure is explained by the theory on the nucleation and growth of crystal, and the low thermal conductivity of oxide ceramic was considered the main factor for it.