Abstract: Modifying and purifying effect of the rear earth(RE) addition on cermet/Cu based alloy composite hardfacing materials were investigated by scanning electron microscope and transmission electron microscope observation as well as calculation of planar lattice disregistry and thermodynamics analysis.The results show that the addition of rear earth as the heterogeneous nuclei of matrix metal is effective and the microstructure of matrix metal can be refined.The RE has a function of deoxidization and purification in liquid metal.The defect of matrix metal can be eliminated and the impact toughness of the composite hardfacing materials can be improved.The RE made a transitional layer with a microcrystalline structure emerged in the interface between cermet and Cu,which enhance the conjoint strength of interface.