Theoretical studies on DNA-cleavage properties of [Cu(bba)(diimine)] 1-4 have been carried out using density functional theory (DFT) and docking methods. The optimized structures of Cu(II) complexes were docked into DNA, glutathiones (GSH), and ascorbic acids (VC) so that the corresponding docking models were obtained. To explore DNA-cleavage properties of Cu(II) complexes, the docking models of complexes with GSH and VC were further optimized using DFT method, while the docking models of complexes with DNA were optimized using QM/MM method because DNA is a supramolecular system. The rate constants ket between complexes and DNA, GSH, and VC, oxidation-reduction potentials of complexes, and binding energies of complexes with GSH and VC were computed. The DNA-cleavage abilities of Cu(II) complexes in the presence VC, GSH, and H2O2 were explored and the experimental results could be reasonably explained. Finally, the DNA-cleavage mechanism of Cu(II) complexes was described in detail, which would contribute to future design of novel anticancer Cu(II) complexes.