A superhard carbon structure (Ibam-C) and its BN phase (Pccm-BN) have been proposed through first principles calculations. The calculated electron bands indicate that both of them are semiconductors. The calculated elastic constants at 0 GPa and phonon dispersion at 0 and 100 GPa confirm that they are mechanical and dynamic stable. The Vickers hardness is calculated to be 78.2 GPa for Ibam-C and 56.7 GPa for Pccm-BN. The calculated ideal strength further confirm their superhardness characteristics.