Abstract: WC-reinforced 18Ni300 steel composite coating was prepared on the surface of Cr5 steel by plasma transferred arc. The influence of adding 25% WC and 35% mass fraction of spherical WC on the microstructure and properties were investigated. The microstructure/phase transformation and properties of the surfacing layer before and after solution treatment (900 °C × 1 h) + aging (490 °C × 5 h) were analyzed and compared. The results show that the addition of WC particles in the maraging steel affects the martensitic transformation in the surfacing structure. The microstructure is mainly austenitic in the WC/MS300 composite surfacing coating. After solution aging heat treatment, the microhardness and wear resistance of WC/MS300 composite surfacing coating were significantly improved, and the microstructure transformed from γ-Fe to α-Fe in the sample, 35%WC coating presented best wear resistance. However, the microhardness and friction and wear properties of the substrate samples decreased. The microstructure evolution of WC indicates that a thick diffusion layer is formed around the WC particles after solution aging heat treatment, which significantly improves the interfacial bonding.