Abstract： Starting from the theory of "internal yang and external yin"， the authors expounded the relation of yin's and yang's essence and their use in human body，and based on this，they analyzed the pathogenesis of yang-deficiency fever and the prescription for it. It was found that the essence of the pathogenesis of yang-deficiency fever lies in the deficiency of yang with exuberance of yin forcing deficiency fire flaming outward. As a result，the treatment of it should be attached great importance to subduing yang and entering yin to make yang return to inner body for future effect，and should treat the root and branch simultaneously. What's more， this paper summarized the experience of treating yang- deficiency fever from principles，methods，prescriptions，and medicine.