Abstract：Objective：To observe the application effect of acupoint application based on the theory of ebb- flow of midnight- midday in bowel preparation for colonoscopy examination. Methods： A total of 218 cases of patients undergoing colonoscopy examination for bowel preparation were selected and divided into the observation group and the control group according to the random number table method， with 109 cases in each group. The control group was given oral administration of Compound Polyethylene Glycol Electrolyte Powder，and the observation group was given acupoint application based on the theory of ebbflow of midnight- midday based on the intervention of the control group. The Boston Bowel Preparation Scale (BBPS) scores， colonoscopy procedure time， intestinal bubble scores， incidence of adverse reactions，and bowel preparation tolerance were compared between the two groups. Results：The scores of the transverse colon， left semi- colon， and right semi- colon and the total scores in the observation group were higher than those in the control group，differences being significant (P＜0.05). The colonoscopy procedure time in the observation group was shorter than that in the control group， and the intestinal bubble score was lower than that in the control group， differences being significant (P＜0.05). The incidences of abdominal distension and bowel discomfort were 22.02% and 6.42% in the observation group， lower than those of 40.37% and 17.43% in the control group， differences being significant (P＜ 0.05). The bowel preparation tolerance rate was 97.25% in the observation group， higher than that of 89.91% in the control group，the difference being significant (P＜0.05). Conclusion：Acupoint application based on the theory of ebb- flow of midnight- midday can improve the intestinal cleanliness in patients undergoing colonoscopy examination， reduce adverse reactions， enhance bowel preparation tolerance， and shorten examination time.