We have put forward a new electron transfer theory: a pair of trivalence rare earthions whose electronic configurations are conjugate may bring about electron transfer andmake the valence state of rare earth ions changed under suitable condition. This variationdistinctly changes the functional properties of materials. So it is important to investigatethe valence changes of rare earth ions for designing new-type function materials. We have put forward a new electron transfer theory: a pair of trivalence rare earthions whose electronic configurations are conjugate may bring about electron transfer andmake the valence state of rare earth ions changed under suitable condition. So it is important to investigate the valence changes of rare earth ions for designing new-type function materials.