Pepsinogen is mainly measured as Pepsinogen I (PGI) and Pepsinogen II (PGII), as well as their ratios, for a total of three numerical indicators. PGI and PGII are proteins secreted by the cells of the gastric mucosa, and about 1% of pepsinogen enters the bloodstream and stabilizes there, and the secretion of pepsinogen changes when the stomach atrophies. PGI is one of the indicators of the function of gastric secretory gland cells. Increased secretion of gastric acid leads to higher PGI values, while decreased secretion of gastric acid or atrophy of gastric mucosal glands leads to lower PGI values. PGII is closely related to gastric fundus mucosal lesions, and if it is elevated, it may indicate that the patient is suffering from fundus glandular duct atrophy, gastric epithelialization, and so on. A progressive decrease in the PGI/II ratio may be associated with disease progression such as gastric mucosal atrophy. When there is a change in the index of pepsinogen, patients should consult the doctor in time and take active treatment.