Objective　 To investigate Diagnosis and examination method of colon endosopy to lower intestinal bleeding .Methods　 The endoscopic materials of 667 cases with lower intestinal bleeding were retrospectively reviewed.Results　 Endoscopy was performed in 667 patients with lower intestinal bleeding ,including little haemorrhage in 547 cases and massive haemorrhage in 120 cases. The 43 cases of massive haemorrhage need the emergency colonoscopy and The 77 cases of that need non-emergency colonoscopy.The positive rate of colonoscopy was 93.5% .The most frequent diseases were colorectal carcinoma、 colorectal polyps、ulcerative colitis in turn,in which the incidences were 38.5%、20.2% and14.7% respectively. The incidence of colonoscopy reaching cecum was 77.5%.The incidence of whole colorectal examination in colorectal carcinoma was only 44。8%(115/257).There were many varieties of pathogenies .The non-emergency colonoscopy in arriving cecum、finding disease and cleaning intestines was obviously superior to emergency colonoscopy(P<0.05,0.001,0.001 respectively). Conclusion The colonoscopy diagnosis to lower intestinal bleeding was the best . The emergency colonoscopy to most of lower intestinal bleeding patient was inferior to the non-emergency colonoscopy and not necessary .