Abstract： Based on the body structure of“internal yang and external yin”， the pathogenesis and treatment of insomnia are explored from the yin and yang mechanism of circadian rhythm. According to the analysis，the essence of the pathogenesis of insomnia lies in yin-yang disharmony，and yang not entering yin. The generation and transformation，and waxing and waning of yin and yang in human body correspond to the changes of waxing and waning of yin and yang in circadian rhythm. When the body breaks the dynamic balance of calm yin and sound yang， it will lead to sleep- wake rhythm disorder. Therefore， in treatment， we should make good use of the method of “warming and subduing” to conduct yang entering yin，and regulate and harmonize yin and yang，so that the body can return to the natural state of yin-yang harmony.