Objective:To evaluate the clinical value of acetic acid and indigo carmine staining in the auxiliary diagnosis of flat gastric lesion. Methods:After conventional electronic endoscopic diagnosis, the patients with flat gastrict lesions were randomly divided into 2 groups,staining group was directly sprayed with acetic acid and indigo carmine, then biopsy, the control group was not stained, determined by the naked eye and conventional biopsy. Results:Two hundred and forty patients were adopted, 120 cases of each group. In the staining group, 18 cases had mucosa discoloration, the detection rate of early gastric cancer and high grade intraepithelial neoplasia was 94.4%(17/18), 79 cases appeared poorly stained, the detection rate of intestinal metaplasia and low grade intraepithelial neoplasia was 91.1%(72/79). In the staining group, 10 early gastric cancers, 25 intraepithelial neoplasia and 58 intestinal metaplasia were found, while in the control group 2 early gastric cancers, 6 intraepithelial neoplasia and 32 intestinal metaplasia were found respectively. Conclusion:Staining with acetic acid and indigo carmine improves the detection rates of early gastric cancer and precancerous lesion in flat gastric lesions, especially in the discoloration and poorly stained areas.