Abstract: Nickel based alloy-WC composite coating with different doped P were prepared on the steel by means of flame brazing. Effects of doped P on microstructure and properties of nickel based alloy-WC composite coating were studied by means of SEM,EDS,Wear test and Rockwell hardness test. The formation mechanism of cracks,slag and gas cavity were explored. The results show that,the hard-phase WC and nickel matrix had good wettability,P doped could obviously accelerate the inter-diffusion between WC and Nickel matrix,resulting in WC embrittlement and crack that forms in the coating,and P was easily oxidized,resulting in porosity and slag that forms in the coating.Crack,slag and gas cavity can reduce the microhardness of coating from 52 HRC to 30 HRC and the wear amount of the coating is increased sharply when P doped is increased from less than 0% to more than 10%. Therefore,doped p can increase the formation of crack,slag and gas cavity in the coating,and consequently reduce the hardness and wear-resistance of the coating.