Abstract: Cobalt based alloy coating was prepared by laser cladding technology. Through a series of preparation and test of the coating, the effects of laser thermal input on the size, dilution rate, microstructure, number of pores and cracks of the coating of cobalt based alloy were studied. The results show that the laser thermal input energy increases from 66.7 J/mm² to 120 J/mm², and the height of the coating decreases gradually. The depth of heat effect decreases at first and then increases, and the dilution rate of the coating has the same trend as the depth of heat effect. The dendrites near the lap surface of the coating are mainly composed of bulk crystals and columnar crystals. At the same time, when the heat input energy increases from 66.7J/mm² to 100 J/mm², the number of pores near the lap surface and the number of cracks in the coating decrease with the increase of heat input. When the heat input energy is greater than 100 J/mm², the number of air holes in the vicinity of the lapping surface and the number of cracks in the coating increase as the heat input increases.