Abstract:Objective?To compare the effect of water-infusion colonoscopy and conventional air-infusion colonoscopy on the bowel cleanliness during withdrawing.?Methods?A single blind randomized controlled trial was conducted. 222 patients were randomly divided into water-infusion group (group A, 112 cases) and air-infusion group (group B, 110 cases). The cleanliness scores, scores improvement, pain scores, time of reaching cecum, depth of colonoscopy, rate of whole colon examination, adenoma detection rate (ADR), operator’s difficulty and complications were compared between the two groups.?Results?The cleanliness score during withdrawing was higher in group A [M(8)/IQR(1) vs M(8)/IQR(2), P = 0.000], the improvement was higher in group A [(0.53 ± 0.74) vs (0.23 ± 0.55), P = 0.000], the abdominal pain score was significantly lower in group A [M(2)/IQR(1) vs M(4)/IQR(2), P = 0.000] and the ADR was higher in group A (36.61 % vs 23.64 %, P = 0.041). The operator’s difficulty evaluation score was significantly lower in group A [M(1)/IQR(1) vs M(2)/IQR(1), P = 0.005]. There were no significant differences at the time of reaching cecum, the depth of colonoscopy and the whole colon examination rate between the two groups. ?Conclusion?Water-infusion colonoscopy could significantly improve the bowel cleanliness during withdrawing scope, improve the ADR and reduce abdominal pain of patients, without increasing the time to reach cecum.