With density functional theory and non-equilibrium Green function method,we calculate I-V characteristics and transmission spectra of deoxyribonucleotides under low bias.Effect of electrode distance on transverse electronic transport is discussed.As distance between electrodes is less than 1.55 nm,it shows great influence on electronic structures.As the distance is more than 1.55 nm,the energy level near LUMO and HOMO changes slowly and the variation of LUMO-HOMO gap is very small.At a fixed distance between electrodes,the relative current of deoxynucleotides is not changed with lower biases (0.1~0.8 V).The current of T and C increases rapidly and is greater than that of A and G as the bias increases from 0.8 to 1.0 V.