Via a reconsideration of a simple model for bipolarons, we have shown that in order to-keep the total energy of the model system to be a stable minimum, a new phonon coherent state should be introduced as a result of the electron-phonon interaction. Thus it could be in-fered that the reduction effect of phonons is much weaker and the range of the singlet bipo-laronic state as the stable ground state configuration is more extensive than what the previous authors considered.