Objective: To observe simethicone emulsion's defoaming effect during colonoscopy and abdominal distention preventing effect after colonoscopy. Methods: 100 patients subject to colonoscopy in our hospital during August 2015 and August 2016 were divided into control group (n=50) or simethicone group (n=50) according to whether or not taking simethicone orally before colonoscopy under patients' intentions. The intracolonic foam, view clearness during colonoscopy, patients' abdominal distention, and colonoscopy manipulators' satisfaction degree were recorded and analyzed. Results: The intracolonic foam was significantly less in simethicone group compared to controlgroup(P<0.05); the two groups had a similar colonoscopy view clearness(P>0.05); patients in simethicone group had significantly less degree of abdominal distention after colonoscopy than those in control group(P<0.05); the colonoscopy manipulators were more satisfied with the procedures in simethicone group than with those in control group(P<0.05). Conclusion: Administrating oral simethicone emulsion to patients 3 hours before colonoscopy yields better defoaming effect, less abdominal distention, and better satisfaction of colonoscopy manipulators.