Abstract: Two types of WC-TiC-TaC-Co cemented carbide blades were failured at different degree in same using process. By the study of chemical composition, microstructure and hardness, it was approved that C5 cemented carbide blade can use no longer than A45 cemented carbide blade. The study results showed that the excess of TaC can not depress the growing of α-phase and promote combination property in three-element cemented carbide. Instead, the brittleness increased and led to early failure of C5 cemented carbide blade.