To investigate the resonance energies and lifetimes of temporary anion states of chloromethanes, long-range corrected density functional theory is adopted in this article. Their values are determined by calculating the density of resonance states via the stabilized Koopmans' theorem. The characteristics of these resonance orbitals are also analyzed. By comparing with experimental values and previous theoretical calculations, our method can yield not only conformable results but also more complete information on the resonance states.