Based on the first-principles method, six interface models of WC-Co/cBN4B, WC-Co/cBN4N, WC-Co/cBN1B-near OA, WC-Co/cBN1N-near OA, WC-Co/cBN1N-near OB and WC-Co/cBN1B-near OB were established, then its interface adhesion work and fracture toughness were calculated. The WC-Co/cBN4B interface has the maximum adhesion work of 9.705 J?m-2, and the interface is the most stable. The work is greater than the fracture toughness of the WC(0001)w interface of 7.824 J?m-2, so the crack tends to appear in the matrix. While the WC-Co/cBN4N interface has the minimum adhesion of 4.470 J?m-2, and the interface is the most unstable. The work is less than the fracture toughness of the WC (0001)w interface, so the crack tends to appear at the interface. Based on this, the charge density difference, density of states and Mulliken population analysis were carried out to explain the interface stability from the deep perspective of charge transfer, bonding mode and valence electron distribution. The results show that:there is charge transfer between Co and B atoms at the interface of WC- Co/cBN4B model, which is hybridized by Co-d and B-p orbital to strong Co-B covalent bond. There is also charge transfer between Co and N atoms at the interface of WC-Co/cBN4N model, which is hybridized by Co-d and N-p orbital to weak Co-N covalent bond. At the interface of the two models, the population of Co-B covalent bonds is larger, the bond length is smaller and the bond energy is larger. The effect of Co-B covalent bonds is stronger than that of Co-N covalent bonds. Therefore, WC-Co/cBN4B has better interface bonding performance and more stable interface.