The original title of this book is Sanyin Jiyi Bingyuan Luncui, abbreviated as Sanyin Fang, written by Chen Yan of the Song Dynasty in the first year of Chunxi (1174).

The main existing versions of this book include: the Southern Song Dynasty edition supplemented by the Yuan Dynasty Masha reprint, the Yuan Dynasty edition, the Japanese Kanbun second year edition, the Japanese K?roku sixth year (1693) Echigo edition, Siku Quanshu edition, the Qing Dynasty Guangxu twenty-third year Qinglianhuaguan edition, the 1934 Shanghai Hongzhang Shuju lithographic edition, and the 1957 People's Health Publishing House lead print edition.

Sanyin Fang consists of 18 volumes and 180 sections. The content covers internal, external, gynecological, pediatric, and five sense organs departments, with over 1050 prescriptions recorded. Although the book is primarily a collection of prescriptions and belongs to the category of formulary books, the theoretical content also occupies a significant proportion. The important features of the book's compilation style include classifying diseases by cause, listing prescriptions according to symptoms, discussing before prescribing, and combining prescriptions with theories. The book not only includes "discussions" under each disease to explore the causes and mechanisms of diseases but also contains numerous specialized medical discussions on physiology, pathology, etiology, diagnosis, and yunqi (five movements and six climates), which are quite enlightening to read.

Chen Yan emphasized that "to treat any disease, one must first understand the cause," pointing out that "there are three causes: internal, external, and neither internal nor external. Internal causes are the seven emotions, external causes are the six excesses, and neither internal nor external causes are those that go against the norm." Chen believed that the three causes can cause diseases individually or in combination, and in the process of the three causes leading to diseases, new pathogenic factors such as blood stasis and phlegm-fluid retention can also arise. Under the guidance of this etiology theory, Chen classified diseases according to their causes: first listing apoplexy, cold in the middle, summerheat stroke, dampness stroke, four properties combined with middle, Bi disease, joint pain, beriberi, common cold, cold-damage disease, summerheat injury, dampness injury, pestilence, malaria, etc., as externally caused; then listing zang-fu organ cold, heat, deficiency, and excess diseases, as internally caused; and finally listing diseases caused by factors such as diet, fatigue, and trauma, such as bleeding and blood stasis, as neither internal nor external causes. This method of classifying diseases by cause has certain significance for deepening the understanding of disease causes and mechanisms and enhancing the specificity of prescription selection and medication use.