Huangdi Neijing. The earliest medical classic Huangdi Neijing in China appeared from the Warring States Period to the Pre-Qin Period. It is one of the four classic works of traditional medicine, which lays a foundation for understanding human physiology, pathology, diagnosis and treatment. It is a medical work with great influence in China and is called the medical ancestor. Huangdi Neijing, referred to as Neijing for short, is the foundation work of China's medical theory and one of the most original medical thoughts. Huangdi Neijing, composed of Su Wen and Ling Shu, was compiled by Bing Wang in the Tang Dynasty and Songshi in the Southern Song Dynasty, and has been handed down to this day. There are 162 articles today. Its completion is a long historical process, and the evolution process is complicated after many times of arrangement. As the originator of TCM constitution science, Huangdi Neijing put forward a variety of constitution classification methods. According to the viewpoint in the book, the formation of human physique is summarized as being influenced by congenital and acquired factors. Huangdi Neijing discusses the formation, changes, characteristics, constitution and health preservation of the human body, and has made great contributions to the development of TCM constitution theory. However, Huangdi Neijing is only a theoretical hypothesis, and there are many wrong views and far-fetched explanations in the book. We must take the essence, discard the dross and test the authenticity of the contents in the book with practice. The completion of Huangdi Neijing is an important milestone in the medical history of China. For thousands of years, Huangdi Neijing has played an important role in people's health preservation, disease prevention and treatment, and has also played an important guiding role in our contemporary health preservation. Its profound and rich connotations and ideas have trained generations of medical experts for China and even the world. However, Huangdi Neijing does not represent the highest level of Chinese medicine. Due to the level of science and technology at that time, Huangdi Neijing could not make a microscopic and detailed analysis of human physiology, which also caused many immature concepts in the book. With the continuous development of science, later generations of Chinese medicine continued to supplement and improve Huangdi Neijing, which made the level of Chinese medicine mature day by day.