Abstract： Using the ontological structure theory of“internal yang and external yin”， from the ontological structure of internal yang and external yin and the driving force of upward and outward movement of yang and downward and inward movement of yin，this paper explains that the essence of the theory of yang is in excess while yin is insufficient put forward by ZHU Zhenheng is kidney essence insufficiency，and deficiency fire flaming upward. It is believed that at present，in clinical practice，there exists many misuses of drugs that clear heat and drain fire， enrich yin and promote fluid production， because of the misunderstanding of the original intention of“yang is often in excess， while yin is often insufficient”by ZHU Zhenheng. Therefore， the methods of supplementing kidney and essence， and returning fire to its source are put forward pertinently.