This article explained Li Dongyuan’s “yin fire” theory based on literature study and clinical practice， and it was believed that the disease of “yin fire” was due to internal injury to diet， fatigue and seven emotions. The “yin fire” was characterized by asthenia fire， with clinical characteristics such as heat manifestitions with internal deficiency， depression and introversion， obvious in the local， and more serious after consumption. Its core pathogenesis was deficiency of qi， deregulation in ascending and descending， and heat depression in the middle jiao. The course of the disease had a tendency from asthenia heat to asthenia cold， and could be divided into qi deficiency yin fire， yin fire with dampness and cold dampness based yin fire. Buzhong Yiqi Decoction， Bupiwei Shengyangqi Xieyinhuo Decoction and Shensheng Fuqi Decoction can be used for the above three stages.