The structure and lattice damage induced by four boron (B) atoms and eight nitrogen (N) atoms with the energy of 500 eV co-doped into diamond films at room temperature are investigated by molecular dynamics simulation based on Tersoff empirical potential. The results show that the distribution of most of vacancies is nearer to the surface than the interstitials. Interstitials arrange in diamond in tetrahedral type (T-type) configuration or dumbbell type (D-type) configuration. Percentage of boron atoms and nitrogen atoms located in substitutional positions are found to be around 78%. The B-N bond length is shorter than C-C bond length in diamond by 13%. B-N bonding helps to reduce the lattice distortion in diamond.