Abstract: The theory of "yang in excess with insufficient yin" is not just closely related to Zhu Dan-xi's study experience and medical practice, but is also inextricably linked to the social background, the theory in Huangdi's cannon of medicine, the ideology of "Yijing", as well as the academic influence of Song and Yuan dynasties. By exploring the connotation of the theory of "yang in excess with insufficient yin", and by considering the background of the time when Zhu Dan-xi proposed it, we can sort out the cultural context and explore the cultural roots, which will be beneficial to the understanding of Zhu Dan-xi's medical thought.