The process of triangular prism formation and abnormal grain growth of WC was modeled using pseudo Monte-Carlo simulation based on atomic adsorption and coalescence mechanism. Grains of WC evolved into the triangular prism shape due to {101￣0} and {12￣10} planes of fast growth rate and subsequent coalescence of {101￣0} and {11￣00} planes were the main reason for the abnormal grain growth. The probability of coalescence computed by the Monte-Carlo method agreed well with the theoretical value. Experimental evaluation of the computational model was made in sintered WC-25wt.%Co alloy. The experimental alloy was made with WC powder of different particle size, 0.8㎛ and 325mesh, respectively, and with two different sintering conditions: solid phase sintering at 1250℃ for 12h and liquid phase sintering at 1370℃ for 72h. The alloy made with the fine powder assumed the triangular prism shape quickly during solid phase sintering, and their growth characteristics could be explained by the atomic adsorption and coalescence models.