In order to improve the wear resistant properties, WC ceramic particles were used to reinforce Hadfield steel. WCp/Hadfield steel composites were fabricated by optimized solid state sintering process of powder metallurgy. Interface structure, constituent phase and the forming mechanism of the composites were investigated systematically. The results show that the WCp/Hadfield steel composites have uniformly distributed particles and well bonded interface between WC particles and Hadfield steel. In the WCp/Hadfield steel composites, the interface between WC particles and Hadfield steel matrix is of shell shape, in which W, Fe and Mn elements diffuse between the two phases. The interface is of metallurgical bond, in which a new phase, namely Fe3W3C is formed. The micro-hardness of the interface layer is between those of WC and the steel matrix, which can provide a guarantee for the property transition between WC particles and Hadfield steel matrix. The diffusion reaction mechanism of the interface was also systematically studied.