Objective To improve WC-coating properties. Methods Fluent software was used to simulate the flame of the high velocity oxygen fuel (HVOF), curves of distance-velocity and distance-temperature of flame were obtained, HVOF in-flight characteristics of WC-17Co powder in 3 different sizes (with average diameters of 21.72 μm, 32.92 μm, 42.56 μm, respectively) was monitored using spray watch, curves of distance-velocity and distance-temperature of WC-17Co powder were obtained, and the effect of flame velocity and temperature on the velocity and temperature of WC-17Co particles was revealed. The splatting and flattening ratio of WC-17Co powder was studied using SEM, the coating porosity of different powder sizes was measured and the compactness was compared, meanwhile, the coatings′ hardness was measured using indentation method. Results The WC-17Co powder′s velocity and temperature increased first and then decreased along with the spray distance, the velocity and temperature values decreased with increasing particle size, depending on different particle sizes, the peak velocity varied from 690 m/s to 810 m/s and the peak temperature ranged from 1890 ℃ to 2050 ℃; smaller particles had a higher flattening ratio after the impact on nickel alloy base, and the ratio varied from 1.94 to 2.35; WC-17Co coating porosity increased with increasing particle size, nevertheless, the Knoop hardness decreased, with values between 1072HK to 1284HK. Conclusion The WC-17Co powder’s velocity and temperature increased first and then decreased during the process of HVOF, and were negatively correlated to the particle diameter; the compactness and Knoop hardness decreased along with the increase of particle diameter.