Reduction of 6,7-dimethoxy-3,4-dihydroisoquinoline with sodium boron hydride in methanol yielded two conformers of 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline. These compounds have been characterized by spectroscopic studies. VT NMR studies suggest that the N-H bond may undergo charge transfer (CT) in variable temperature. It is concluded that the lone pair electron in the equatorial position is predominate under longer reaction time or lower temperature condition.