Abstract: Tungsten carbide (WC) layer was in-situ synthesized at the surface of HT300 gray cast iron by combination of casting-infiltration and heat treatment process. The microstructures and wear resistance of the WC layers were studied by scanning electron microscopy, X-ray diffraction and pin disk abrasive wear test. The wear mechanism was also analyzed. The results show that the WC layer with thickness of 112 μm was formed on the surface of the gray cast iron. The relative wear resistance of the WC layer first increased then decreased with the increase of loads. When the load was 15 N, the relative wear resistance of the WC layer was better than that of the gray cast iron. Under the heavy load, the wear-out failure of the WC layer mainly ascribed to particles′ squeezing fracture and partial peeling, meanwhile sheet-like wear debris was generated.