In this study, the synthesized WC-8Co composite powder with the particle size of 100nm, 250nm, and 400nm were added to the coarse WC/Co powder respectively. The mixture was sintered at different temperature with Ar atmosphere. The morphology, grain size and its distribution of the sintered bulk were studied. The WC grain growth mechanism of the samples with composite powder additives at different sintering stage was analyzed. It was found that the ultra-coarse cemented carbide was prepared by WC/Co mixed powder with nanometer or submicron particle size composite powder additives. Especially, the cemented carbide with a grain size 9.3μm was prepared using the mixed powder with the nanocomposite powder additives as raw material. At the initial sintering stage, the addtion of the namometer and ultrafine composited powders increases the surface energy of the mixed powders obviously, which is benefit to promote the growth of WC grains effectively. During the liquid sintering temperature, the sintered bulks with the nanocomposite powder have a larger dissolution driving force, which causes the small grains to dissolve and precipitate on the surrounding large grains, further increasing the grain size of the sintered bulks. In the bulks where the ultrafine composite powder was added, the small grains WC are concentrated and the dissolution driving force is small, and the precipitation mainly occurs in the surrounding small grains between, the dissolved precipitation to achieve a dynamic equilibrium, so that the average grain size of sintered bulk grows slowly.