Based on non-equilibrium Green's function and first-principles calculations, we investigate the electronic transport properties of 4,4'-biphenyl bis (dithiocarboxylate) (BDCT) molecular junction with the field-induced geometry relaxation. The results indicate that the external field has noticeable effects on the molecular structure, coupling strengths and bonding distances. More importantly, it is found that the inclusion of field-induced molecular geometry relaxation can predict a current-switch behavior, which may have some potential applications in future molecular circuit. (C) 2009 Elsevier B. V. All rights reserved.