Zuoguiyin， which first recorded in Jingyue Quanshu written by ZHANG Jiebin in the Ming dynasty， was included in the Catalogue of Ancient Famous Classical Formulas（The Second Batch）. This study followed the Principles of Textual Research on Key Information of Ancient Famous Classical Formulas to determine the key information of Zuoguiyin in ancient and modern literature， such as the formula origin， the composition of the formula and the origin of the drugs. It was found that the composition， dosage， preparation and processing methods of Zuoguiyin were basically the same as the original formula. The original dosage of this formula is 41.03 g of Rehmanniae Radix Praeparata（the fresh or dried tuberous roots of Rehmannia glutinosa， processed by wine stewing or wine steaming）， 7.46 g of Dioscoreae Rhizoma（the dried rhizomes of Dioscorea opposita）， 7.46 g of Lycii Fructus（the dried mature fruit of Lycium barbarum）， 3.73 g of Glycyrrhizae Radix et Rhizoma Praeparata cum Melle（the dried roots and rhizomes of Glycyrrhiza uralensis， processed by honey-roasted method）， 5.595 g of Poria（the sclerotium of Poria cocos）， 5.595 g of Corni Fructus（the dried mature fruit pulp of Cornus officinalis）. The method of administration is to add 600 mL of water to all the herbs， decoct to 140 mL and take before meals. The function of Zuoguiyin is to nourish Yin and tonify the kidney， and it is often used in the treatment of lumbar soreness and ejaculation， night sweating， dry mouth and throat， thirst and desire to drink， glossy red tongue， thin and rapid pulse， etc. Since ancient times， Zuoguiyin has been used to treat a variety of internal and gynaecological diseases as well as diseases of the nervous， circulatory and reproductive systems that are predominantly caused by kidney Yin deficiency. However， there is not much research on the modern application and therapeutic mechanism of this formula， and there is no standardized preparation in the market， so the degree of development and utilization is not high， and there is still a lot of room for research.