Objective To explore the effects of medication interval on the quality of split-dose bowel preparation and analyze the independent risk factors affecting the quality of bowel preparation. Methods This pilot study involved two centers. Adult outpatients who underwent screening, surveillance, and diagnostic colonoscopy in the First Affiliated Hospital of Naval Medical University (n=46) and the Fifth Hospital of Zhangjiakou (n=20) between April and June 2023 were enrolled. Bowel preparation was conducted based on the guideline. Patients were divided into the short-interval group (4-<10 hours, n=45) and the long-interval group (10-16 hours, n=21) based on the time between the two administrations of polyethylene glycol during bowel preparation. Differences in terms of patient-reported outcome measurements (patient-reported willingness to repeat the bowel preparation regimen, satisfaction with bowel preparation, satisfaction with sleep), defecation frequency, Boston bowel preparation scale scores, bowel preparation bubble scores, bowel preparation qualified rates, polyp detection rates and incidence of adverse events were compared. Relevant factors influencing bowel preparation quality were analyzed by univariate logistic regression. Results There were no significant differences in patient-reported willingness to repeat the bowel preparation regimen [88.9% (40/45) VS 85.7% (18/21), χ²<0.001, P>0.999], the satisfaction with bowel preparation [65.9% (29/45) VS 57.1% (12/21), χ²=0.469, P=0.493], or the satisfaction with sleep quality [35.6% (16/45) VS 28.6% (6/21), χ²=0.314, P=0.575] between the short-interval and long-interval groups. Similarly, no significant differences were observed between the groups in defecation frequency (11.3±4.8 VS 10.2±4.4, t=0.861, P=0.395), Boston bowel preparation scale scores (8.2±1.4 scores VS 7.9±1.2 scores, t=1.024, P=0.311), bowel preparation bubble scores (8.6±1.0 scores VS 8.4±1.5 scores, t=0.672,P=0.506), bowel preparation qualified rates [88.9% (40/45) VS 90.5% (19/21), χ²<0.001, P>0.999], polyp detection rates [33.3% (15/45) VS 47.6% (10/21), χ²=1.242, P=0.265], or incidence of adverse events [24.4% (11/45) VS 14.3% (3/21), χ²=0.381, P=0.537]. Univariate logistic analysis suggested that a low-fiber diet (OR=8.100, 95%CI:1.400-46.849, P=0.019) was an influencing factor for qualified bowel preparation. Conclusion Medication interval of the two doses of polyethylene glycol in a split-dose bowel preparation regimen for colonoscopy has no significant impact on bowel preparation quality. Notably, preoperative low-fiber diet emerges as an independent protective factor for qualified bowel preparation.