Considering the effect of molecular vibrational levels, inelastic currents through the "metal/single molecule/metal" in the frame of normal vibrational mode are studied. The results show that the Franck-Condon blockage is strongly dependent on the stable energy configuration of molecule in the charge transmission, thus the relation between stationary state and Franck-Condon blockage and the relations of intra molecular vibrational redistribution as well as the relative position of molecule and electrodes to the current-voltage character of the stationary molecule state are further studied theoretically.