Three predicted new two-dimensional (2D) boron carbon nitrogen (BCN) structures, named B 8 C 2 N 8 , B 6 C 6 N 6 -1, and B 6 C 6 N 6 -2, are investigated theoretically. The stability and electronic properties of the three structures are explored. The results reveal that three 2D BCN structures are dynamically, thermodynamically, and mechanically stable. B 8 C 2 N 8 is a direct semiconductor with a band gap of 1.76 eV, B 6 C 6 N 6 -1 is an indirect semiconductor with a band gap of 0.21 eV, and B 6 C 6 N 6 -2 exhibits metallic properties. B 6 C 6 N 6 -1 shows a transition from semiconductor to conductor under an external strain. The large adsorption energies of TNT adsorbed on BCN reveal that it is feasible to use 2D BCN materials to adsorb TNT. Among the three BCNs, due to the largest band gap variation and the largest charge transfer amounts, B 8 C 2 N 8 has an outstanding performance in terms of the adsorption of TNT and is expected to be used to detect TNT or other nitro molecules.