Precancerous lesion is a pathological term that refers to certain lesions with obvious risk of cancer, which may turn into cancer if not treated in time. The study of precancerous lesions of gastric cancer is important for the early detection of gastric cancer. It can not only understand the process of gastric cancer and environmental factors from the study of precancerous lesions, but also the follow-up of such lesions can detect early gastric cancer in time. Then, what is precancerous lesion of gastric cancer? As precancerous lesions of gastric cancer are naturally lesions of gastric mucosal epithelial cells, such as various precancerous diseases we know: chronic atrophic gastritis, gastric ulcer, gastric polyp, etc., although they are all different diseases, the basis of their occurrence of gastric cancer is gastric mucosal epithelial cells. Most scholars believe that precancerous lesions of gastric cancer are mainly heterogeneous hyperplasia of gastric mucosa epithelium. It is difficult to determine whether intestinal epithelial hyperplasia of gastric mucosa, as a major lesion component of chronic atrophic gastritis, is a precancerous lesion, but it has a close relationship with gastric carcinogenesis, which is widely agreed. There are many current terms that fall within the scope of precancerous lesions, such as heterogeneous hyperplasia, atypical hyperplasia, and intraepithelial noninvasive neoplasia, which are confusing in use. Although the WHO tumor classification published in 2000 has clearly classified precancerous lesions of gastric mucosa into two grades, low grade and high grade intraepithelial neoplasia, according to the degree of cellular heterogeneity and structural disorder, there are still diagnostic inconsistencies in the process of implementation, so the experts convened two international conferences to discuss the classification and diagnostic criteria of gastric mucosal intraepithelial neoplasia and early carcinoma. Finally, at the second international conference in Vienna, a more unanimous opinion was reached, that is, the series of changes in gastric mucosa from reactive hyperplasia to invasive carcinoma was divided into five categories: reactive hyperplasia, indeterminate intraepithelial neoplasia (i.e., it is difficult to distinguish whether it is reactive hyperplasia or heterogeneous hyperplasia), low-grade intraepithelial neoplasia, high-grade intraepithelial neoplasia and invasive carcinoma. Even suspected invasive carcinoma is clearly classified as high-grade intraepithelial neoplasia, which is collectively called high-grade intraepithelial neoplasia. Currently, there is no uniform guideline for the management of low-grade intraepithelial neoplasia, and most scholars recommend close and regular endoscopic follow-up without special management. Since high-grade intraepithelial neoplasia is very closely related to invasive carcinoma, surgical resection is preferable once the diagnosis is made.