The Diluent NaCl was introduced into the WO3-Mg-C-Na2CO3 system (WO3, C, Mg powders and Na2CO3) to prepare submicron tungsten carbide (WC) powders via salt-assisted combustion synthesis. The products were analyzed by SEM, EDS and XRD, and effect of C content on morphology, average particle size and phase composition of the products were studied. The Results show that on basis of the m = 0.125 (the number of moles of Na2CO3), when the number of moles of carbon in raw material increases from l=2 to 2.25 and 2.5, respectively, before leaching, the product was made up of a small number of large size particles and a large number of small size particles; After leaching, samples were composed of aggregates of submicron particles, the fusion sintering phenomenon between particles was very weak, indicating low degree of aggregation. Particle size distribution of leached product almost falls into the normal distribution, and the particle sizes range from 200 nm to 350 nm. Under the condition of l=2.25, a main target product is WC, and content of by-products W2C is extremely few. That is, k = 2.0 (the number of moles of NaCl), m = 0.125, and l=2.25 are the process conditions for single-phase WC synthesis.