What is the earliest Chinese medicine book in China?

China's earliest TCM work is Huangdi Neijing, which is one of the four classic TCM works (Huangdi Neijing, Treatise on Febrile Diseases, Synopsis of the Golden Chamber, Treatise on Febrile Diseases), the first masterpiece handed down in the name of Huangdi, the ancestor of the Chinese nation, and the earliest medical work in the medical treasure house of China. It is a medical masterpiece that studies human physiology, pathology, diagnostics, therapeutic principles and pharmacology. Theoretically, the theories of yin and yang, five elements, pulse condition, Tibetan image, meridians, etiology and pathogenesis, symptoms, diagnosis, treatment, health preservation and luck are established. His medical theory is based on China's ancient philosophical theory, which embodies China's naive dialectical thought in ancient times.