Objective:To explore the influencing factors of bowel preparation quality in hospitalized elderly patients, and to find the appropriate waiting time from the end of bowel preparation to the beginning of colonoscopy.Methods:Baseline and clinical data of elderly patients over 60 years old who underwent colonoscopy in the Tenth People′s Hospital, Tongji University from February 2021 to August 2021 were collected. Multivariate analysis was used to screen the factors that might affect the quality of bowel preparation in hospitalized elderly patients. Patients were grouped according to waiting time before colonoscopy. After eliminating confounding factors using propensity matching analysis, the difference of bowel preparation quality among groups was compared.Results:251 patients were included in the study. Multivariate analysis revealed that, hypertension ( OR=3.530, 95% CI 1.295-9.618), chronic constipation ( OR=3.302,95% CI 1.132-9.632), dietary compliance ( OR=0.161, 95% CI 0.070-0.371), medication and drinking water compliance ( OR=0.167, 95% CI 0.070-0.397), exercise compliance after medication ( OR=2.245, 95% CI 1.040-4.845), The frequency of defecation after medication ( OR=0.446, 95% CI 0.308-0.647) and waiting time ( OR=0.537, 95% CI 0.387-0.745) were important factors affecting the quality of bowel preparation in hospitalized elderly patients ( P<0.05). There were differences in bowel preparation quality between groups of waiting times. The overall quality of bowel preparation in 120-180 min group was significantly better than that in 241-300 min group, 301-360 min group and>360 min group ( P<0.05). The overall quality of bowel preparation in 181-240 min group was better than that in >360 min group ( P<0.05). There were no significant differences among other groups( P>0.05). The scores of cecum and ascending colon were the best in 120-180 min group, and the cleanliness of descending colon, sigmoid colon and rectum was significantly higher in 241-300 min group, 301-360 min group and > 360 min group. The scores of descending colon, sigmoid colon and rectum showed that the intestinal preparation quality of 181-240 min group was better than that of 301-360 min group and > 360 min group. Conclusions:The best examination time for elderly patients is about 180 minutes after bowelpreparation. Medical workers should flexibly guide the medication time to ensure that patients are in the best clean state of intestinal tract during examination.