Ab initio calculation shows that the ideal strength of C-BN phase in the [111] direction has lower values, which signifies first cleave in the (111) plane under tensile loadings. It is found that C-BN phase possesses a stronger covalent bonding and wide bandgap. In addition, a combination of first principles calculation and quasi-harmonic Debye model are extremely useful in studying thermodynamic and elastic properties of C-BN phase within the temperature range of 0–2000K. The calculated results are in good agreements with experimental observations in the literature, and are discussed in terms of electronic structures, heat of information and ideal strength.