Abstract: Objective To observe the effect of Senna Granules combined with polyethylene glycol electrolyte solutions(PEG-ELS)in bowel preparation for colonoscopy. Methods A total of 174 patients with colonoscopy were randomly divided into three groups with 58 cases in each group, including PEG-ELS 2 L group, PEG-ELS 3 L group and combination group. The quality of bowel preparation, endoscopic time, adenoma detection rate and adverse reactions were compared among the three groups. Results The intestinal cleanliness scores of the combination group and the PEG-ELS 3 L group were significantly higher than those of the PEG-ELS 2 L group(P<0.05 or P<0.01). The qualified rate of intestinal preparation in the PEG-ELS 2 L group was 70.70%, which was significantly lower than 91.40% of the PEG-ELS 3 L group and 93.10% of the combination group(P<0.05 or P<0.01). The average time into terminal ileum in the combination group was(4.80±0.31)min, which was shorter than(5.58±0.34)min in the PEG-ELS 2 L group and(5.49±0.41)min in PEG-ELS 3 L group, but there were no significant differences(P>0.05). There were no significant differences in bubble scores of left colon, right colon and transverse colon and total bubble score among the three groups(P>0.05). The detection rate of adenomatous polyps in the combination group was significantly higher than that in the other two groups, but there was no significant difference(P>0.05). The incidence of adverse reactions in the combination group was significantly lower than that in the PEG-ELS 3 L group(P<0.05). Conclusion Senna Granules combined with PEG-ELS can improve the quality of bowel preparation and the detection rate of adenomatous polyps, and will not prolong the time into terminal ileum and increase occurrence of adverse reactions.