 Helicobater pylori plays an important role in the development of gastric cancer. Eradication therapy can reducing the morbidity of gastric cancer, but cant totally prevent it especially when atrophy and more serious precancerous lesions already happened. Prior studies found the gastric bacterial difference among gastritis, intestinal metaplasia and gastric cancer. However, they didnt reach an agreement. Correas model is widely accepted in the development of gastric cancer. The pathological change makes a more suitable environment for bacteria to overgrowth. This study are designed to analyze the gastric microbial difference of non-atrophic gastritis, atrophic gastritis, intestinal metaplasia, intraepithelial neoplasia and gastric cancer. 