The origin of the rubber-like behavior in mono-domain Au-Cd martensite was explained in terms of a new model that focused attention on the change of long-range elastic interaction energy among vacancies during a domain reversion. Vacancies in martensite, the lower-symmetry phase, produce stress fields with lower symmetry. During martensite aging, vacancies tend to rearrange themselves to lower elastic interaction energy. The low-symmetry elastic field results in a low-symmetry vacancy configuration. When a stabilized martensite domain reverts to a new domain (twin) under external stress, the original vacancy configuration is inherited to the new domain, but such a configuration becomes a high energy configuration because of the lower symmetry of elastic field, and thus it tends to restore the original configuration by reverse twinning. The above vacancy reconfiguration model is consistent with the fact that the rubber-like behavior is closely related to vacancies.