Electronic structure, hardness and optical properties of four crystal structures of z-BC2N and z-B2CN were studied in this paper by first-principles calculations of plane wave ultra-soft pseudo-potential method based on the density functional theory (DFT). Deep analysis of electronic structure was carried out, indicating that z-BC2N(1) and z-BC2N(2) are indirect and direct wide band gap semiconductor, and band gap are 3.381 eV and 2.449 eV respectively, but z-B2CN(1) and z-B2CN(2) are conductors. Furthermore z-BC2N(1), z-BC2N(2) and z-B2CN(1) are superhard materials. Finally, the optical properties of z-BC2N(1) and z-BC2N(2) were analyzed by calculating the relationship between the basic optical function and photon energy of z-BC2N. Those data indicate that z-BC2N structures can be served as wear-resistant materials and high-temperature-resistant materials that used by control windows.