The correlation among composition, structure, chemical bond and thermoelectric property of boron carbide, phosphide and arsenide is studied with SCF-DV-X_α method, one of calculation methods of molecular orbital in quantum chemistry. The differences between the three materials are studied. As the P-P and As-As chains have no characteristic of double bond, it is difficult for the boron phosphide and arsenide to transfer electrons, though they have the same structure as boron carbide. The C-B-C and C-B-B chains have the characteristic of double bond, so it is easy for the boron carbide to transfer electrons and hop the bipolarons. Therefore, boron phosphide and arsenide have no characteristic of double bond but boron carbide has, which is the main reason that as their thermoelectric property is too bad, boron phosphide and arsenide are not considered as the thermoelectric materials, but boron carbide has the much better thermoelectric property than boron phosphide and arsenide.