The WC bulk was in-situ synthesized with mixed WO3 +14.5%C powders by spark plasma sintering at different temperatures. The chemical valence state of W, C, O in the samples were investigated by XPS. The results indicates that the element W changes from W+6, W+5, W+4 in oxidative state to metallic W0 and W+2 in carbide state with the rising of synthesizing temperature. It reveals that WO3 is firstly reduced by carbon to form intermediate tungsten oxides such as WO2.72, WO2, and metallic W in the reduction process, then the carbonization reaction occurs, and the WC is formed finally.