In order to solve the decarburization problems of WC particles caused by high temperature during detonation spray process, a detonation spraying facility with Laval nozzle was designed. Theoretical and experimental studies on preparing WC coatings via detonation spraying were carried out by introducing that facility. Numerical calculation results based on isentropic flow indicated that the temperature of the carrying gas could be decreased greatly by introducing nozzle, meanwhile, the velocity of the WC particles could also be accelerated up to above 1000m/s. Some pressure sensors were used to test the pressure in the entrance and the exit of the nozzle, the Mach number of the gas was calculated. Laser Extinguish method was employed in the nozzle exit to measure the average velocity of the particles. Both theoretical and experiment results could match each other properly. SEM, metalloscope and XRD were used to characterize WC particles and the coatings. The test results presented that the Laval nozzle could avoid decarburization phenomenon of WC particles effectively. This paper provides a new thought to solve the decarburization problems of WC particles during detonation spraying process.