The internal diseases of TCM include two categories: exogenous and endogenous diseases. The exogenous diseases refer to febrile diseases that are mainly caused by the invasion of exogenous cold, wind-heat, summer-heat,damp-heat, etc, and can be differentiated and treated according to the theory of six meridians, theory of wei, qi,ying and blood, and theory of triple energizer.

The endogenous diseases include diseases of internal organs and meridian system that are mainly caused by endogenous pathogenic factors. They can be differentiated and treated according to the theory of zang-fu organs, theory of qi, blood and body fluid, and meridian theory.