Kidney essence, the essence in the kidney, is originated from prenatal essence and nourished by postnatal essence. It is primarily involved in promoting growth, development and reproduction. Originated from the reproductive essence, prenatal essence is the hereditary substance endowed by parents and stored in the kidney upon birth. Postnatal essence is the nutrient substance acquired from the nutrients of food and drinks and transformed via zang- fu organs’ physiological activities. Kidney essence is formed on the basis of prenatal essence plus the nourishment of postnatal essence. With constant nurturing and nourishment of postnatal essence, prenatal essence could fully implement its role; with the aid of original qi transformed from prenatal essence, postnatal essence could constantly take in nutrients and fulfill transformation.