Abstract: Based on the excellent structural/functional properties of particle-reinforced nickel-based composites, they have a wide application prospects in aerospace, nuclear power, military industry and electronics. The internal heterogeneous interface connection mechanism, reinforcement mechanism and fracture behavior of the tungsten carbide (WC) particle-reinforced IN718 composites (WC/IN718) prepared by using the mechanical ball grinding powder+selective laser melting (SLM) was analyzed. The results show that with the increase of WC particles content (0wt%-20wt%), the specimen is well-formed, WC particles are evenly distributed inside the matrix and no defects at the heterogeneous interface, carbon-poor W₂C layer and carbide layer are produced at the interface, and the matrix alloy mainly grows at the form of columnar crystals. Due to the different energy density distribution within the melting pool, the fracture mode of WC particles at the low temperature position is that firstly the interface reaction layer form at the periphery of WC particle and then WC are fractured by thermal stress. However, WC particles at the high temperature position preferentially break into small particles in size, and then the interface reaction layer is formed with the molten matrix alloy, which is distributed within the matrix. As the content of WC particles increases, the strength of composites tends to increase, while the fracture toughness is reduced, and the tensile strength can be up to 1280 MPa. The reinforcement mechanism is mainly the load transfer effect, the fracture mechanism is the brittle fracture of WC particles and the toughness fracture of matrix alloy.