Each Zang-Fu organ has its own physiological characteristics. The relationships of inter-promotion and inter-restraint exist among the Zang-Fu organs. Compatibility of formula can be modified according to physiological characteristics of the Zang and Fu organs and the relationships of inter-promotion and inter-restraint among the Zang and Fu organs. The Zang and Fu theory is an effective way to research the compatibility of formula and guide its clinical modification.