Abstract: In-situ synthesis of W_xC particle reinforced Ni-base composite coating was synthesized on 316L stainless steel by plasma transferred arc welding. Microstructure, phase constitent, the distribution of reinforced particle, microhardness and cavitation erosion property were investigated by using SEM, EDS, XRD, microhardness tester and ultrasonic vibrator, respectively. Results indicate that Colmonoy 88 coating exhibits a perfect plasma hardfacing tracks and the microstructure is dense. When the molten pool temperature is below 1 655 K, WC and W₂C reinforced particles are in situ synthesized during the melting process. When the molten pool temperature is higher than 1 655 K, the in situ synthesized WC particles are dissolved. The phase constituents of the coating are mainly composed of γ-Ni solid solution, in-situ synthesized W_xC particles and a small amount of Cr₇C₃, Fe₃W₃C and CrB₂. The average microhardness of the coating is 1 619 HV, which is 8 times than that of the substrate. The cavitation erosion resistance of the Ni based composite material is 5 times than that of the substrate in 3.5% NaCl solution.