Qi transformation refers to various transforming changes caused by qi, i.e., metabolism and inter-transformation of essence, qi, blood, and body fluids. Therefore, qi transformation is the metabolic process in human body whereby the substance and energy transformation takes place, and thus it is the root of life activities. Zang-fu organs play an indispensable role in activating and maintaining qi transformation, whose normal function depends on inter- regulation of physiological activities among zang-fu organs. Constant substance exchange between nature and human body is indispensable to maintaining life activities.