The plastic deformation in tungsten carbide plays an important role in the improvement of toughness of cemented carbide. Twining is one of typical ways of plastic deformation. The microstructure and twin deformation proporties of WC phases were investigated by loading alloy specimen. The results show that when WC phase is pure phase, it can generate twin-slip coordination deformation, thus the alloy exhibits higher toughness. And this kind of alloy is possessed of excellent properties during operation, especially in the fields of rock drilling.