A withdrawal time of at least 6 minutes has been considered to be necessary to guarantee the adenoma detection rate and the critical quality criterion of colonoscopy. However, several large observational investigations demonstrated that 9 minutes will be in favor of higher adenoma detection rate and lower risk of interval colorectal cancer, when compared with 6-minute withdrawal. Meanwhile, a few studies also indicated that no significant benefit were observed in longer withdrawal time. Up to now, no randomized controlled trials have been conducted to give a definitive conclusion. Therefore, we performed a multicenter, prospective, randomized Controlled trial to compare adenoma detection rate of 6-minute and 9-minute withdrawal in colonoscopy.

Inclusion Criteria:

• Patients whose age is between 40-85.
• Patients who have indications for screening, surveillance and diagnostic colonoscopy.
• Patients who have signed inform consent form

Exclusion Criteria:

• Patients who have undergone colonic resection
• Patients with intracranial and/or central nervous system disease, including cerebral infarction and cerebral hemorrhage.
• Patients with severe chronic cardiopulmonary and renal disease.
• Patients who are unwilling or unable to consent.
• Patients who are not suitable for colonoscopy
• Patients who received urgent or therapeutic colonoscopy
• Patients with pregnancy, inflammatory bowel disease, polyposis of colon, colorectal cancer, or intestinal obstruction
• Patients who are taking aspirin, clopidogrel or other anticoagulants
• Patients with Aronchick score > 3