The Preface to Shennong's Classic of Materia Medica classifies 365 kinds of drugs based on the idea of skill and number, aiming at systematically sorting them out in 365 days a year. This classification divides drugs into upper, middle and lower categories, and each category has different performance and efficacy. For example, "taking medicine" is mainly for life-saving, non-toxic, and long-term use does not hurt people; "Chinese medicine" is mainly nourishing, which is non-toxic; "Prescribing drugs" mainly treats diseases, mostly toxic drugs. This classification method provides a theoretical basis for drug use and lays a foundation for pharmacology. The whole "Shen Nong Ben Cao Jing" contains rich drug theories, especially the preface, which summarizes all aspects of pharmacology and lays the foundation for the development of pharmacology in later generations.