Abstract: Using SEM, X-ray and EPMA, the heat damage characteristic and mechanism of WC cemented carbide in the course of hadfacing have been investigated. The results showed that the heat damage of cemented carbide was inevitable. The main characteristic of heat damage was the decompose and diffusion of carbide. The grain of fringe carbide grew up, reseparated out and a new phase was formed. The type of heat damage for WC cemented carbide was melting and dissolve of carbide, diffusion and reaction of element. The mechanism of heat damage for cemented carbide was the element diffusion and chemical reaction between cemented carbide and matrix metal. The diffused zoom and new phase were formed at the interface of cemented carbide and matrix. The kind, size, content and method of hardfaceing all directly affected the level of heat damage.