Using the three-dimensional tight-binding model and the matrix transfer method， effects of interfacial couplings on the charge transport properties of DNA molecule have been studied. The results indicate that when the interfacial couplings are ideal， both transmission coefficient and localization length of electrons are larger， the molecule shows higher conductivity， while the case is the contrary when the interfacial couplings are unideal. When the molecule and the metallic electrodes couple ideally， through voltage-current characteristic， it is found that the onset voltage of poly(dG)-poly(dC) DNA is lower than that for the poly(dA)-poly(dT) counterpart， and the current of the former is larger than that of the latter under the same bias voltage， so the conductivity of poly(dG)-poly(dC) DNA is higher than that of the poly(dA)-poly(dT) counterpart.