The theory of Yin-Yang and Five Elements is China's simple dialectical materialist philosophy in ancient times. Therefore, ancient physicians used the theory of Yin-Yang and Five Elements to explain various physiological and pathological phenomena of human body, and guided and summarized medical knowledge and clinical experience, and gradually formed a theoretical system of traditional Chinese medicine based on the theory of Yin-Yang and Five Elements. Yin-yang theory is a theory that discusses the physiological function and pathological changes of human body according to the phenomena and laws of natural movement changes, so as to explain the functional activities, organizational structure and their relationship of human body. The theory of Yin and Yang is China's simple theory of unity of opposites in ancient times, which is based on the monism of Qi. It belongs to the category of China's ancient materialism and dialectics, and embodies the unique dialectical thinking spirit of the Chinese nation. Its philosophy is metaphysical and reflects the model of the universe. Its influence is far-reaching and huge, and it has become the norm of people's behavior. For example, The Art of War, which won the admiration of the world today, is a summary of China's ancient military strategist's theory and practical experience. It applies the meaning of yin and yang to the extreme of military behavior, reaching a superb level.

Yin-yang theory holds that the world is a material whole, and everything in the universe not only has the unity of opposites of Yin and Yang, but also its occurrence, development and change are the results of the unity of opposites of Yin and Yang.

Traditional Chinese medicine applied the theory of yin and yang to medicine, which formed the theory of yin and yang in traditional Chinese medicine and promoted the formation and development of the theoretical system of traditional Chinese medicine. The theory of Yin and Yang in TCM is one of the foundations and an important part of the theoretical system of TCM, and it is a key to understand and master the theoretical system of TCM. "Knowing Yin and Yang is like confusing, like waking up from a dream" (Lingshu Disease Biography), "If you can understand Yin and Yang, you will think more than half" (Jing Yue Quan Shu Zhong Chuan Lu Yin and Yang).

The theory of Yin and Yang in TCM expounds the origin and essence of life, the physiological function and pathological changes of human body, and the basic laws of disease diagnosis and prevention, which runs through the principles, methods, prescriptions and drugs of TCM and has been effectively guiding practice for a long time.