Objective To investigate the effects of Helicobacter pylori (HP) radical treatment on diagnosis of early gastric cancer using conventional white light endoscopy (WLE), chromoendoscopy of indigo carmine dye added to acetic acid, and magnifying endoscopy with narrow band imaging (ME-NBI). Methods Between January 2013 and March 2018, patients without HP (successful cured before six months) or with HP (no radical treatment for HP in recent 6 months), who underwent endoscopy examinations in the Department of Gastroenterology of Ezhou Hospital, People′s Hospital of Wuhan University or the Department of Gastroenterology of Union Hospital, Tongji Medical College Huazhong University of Science and Technology were enrolled in the study. Endoscopy examinations were performed according to the order of conventional WLE, chromoendoscopy using indigo carmine dye added to acetic acid, and ME-NBI. Among the patients finally diagnosed as early gastric cancer by histopathology, 120 patients without HP and 120 patients with HP were continuously collected, and included in the radical treatment group and the non-radical treatment group, respectively. Diagnostic reliabilities of WLE, chromoendoscopy, and ME-NBI for early gastric cancer between the two groups were statistically analyzed. Results There were no statistical differences between the two groups in terms of hospital source (χ2=2.637, P=0.104), gender composition (χ2=0.074, P=0.785), mean age (t=0.582, P=0.561), and lesion morphology (χ2=0.179, P=0.914). The detection rates of early gastric cancer in the radical treatment group using WLE [75.0% (80/120) VS 81.7% (98/120), χ2=7.046, P=0.008], chromoendoscopy [57.5% (69/120) VS 93.3% (112/120), χ2=41.554, P<0.001], and ME-NBI [90.0% (108/120) VS 98.3% (118/120), χ2=7.585, P=0.006] were significantly lower than those in the non-radical treatment group. In the radical treatment group, chromoendoscopy had the lowest detection rate of early gastric cancer, followed by WLE (χ2=2.142, P=0.143) and ME-NBI (χ2=32.736, P<0.001), while ME-NBI had the highest detection rate of early gastric cancer, which higher than that of WLE (χ2= 19.247, P<0.001). Conclusion The diagnosis of early gastric cancer by WLE, chromoendoscopy using the indigo carmine dye added to acetic acid and ME-NBI becomes more difficult after radical treatment of HP. Among the above three endoscopic methods, ME-NBI has the highest diagnostic efficacy, and becomes the first choice for the clinical diagnosis of early gastric cancer after radical treatment of HP.