Based on the renormalization effect of the phonon ground state on the tunneling parameters, a new method is proposed to investigate the localization-dislocalization transition of a tunneling system with bosonic bath. Our study shows the previous theories are in principle built on the displaced phonon state approximation, while our method may be used to examine the effects of other type of phonon ground states (such as squeezed phonon state) on the localization-dislocalization transition.