Cell cycle distribution, cell proliferation index (PI) and DNA index (DI) were analyzed with flow cytometry (FCM) to study changes in human embryo fibroblast exposed to drinking water in gastric cancer prevalent areas for a long time. Results showed both proportion of cells in S and G2M phases and PI increased significantly, DI were beyond its normal range, and cells revealed morphologically abnormal. It suggests drinking water in gastric cancer prevalent areas may contain carcinogenic substances, and correlate closely to high incidence of gastric cancer.