Objective To verify the significance of transabdominal ultrasound measurement of transverse rectal diameter(therectumdiameterRD)in the diagnosis of cystorectal dysfunction（BBD）in children，and to explore the value of clinical interpretation combined with ultrasound imaging in the selection of diagnosis and treat⁃ ment. Methods A total of 167 children with suspected BBD in the urology clinic of our hospital from July 2020 to April 2022 were selected as the observation group，all of them had a history of abnormal urination and defecation， and the abnormalities of body anatomy and nervous system were excluded. 46 parents with obvious symptoms were selected to fill in the BBD questionnaire. 172 healthy children in the same period were selected as the control group，all of them had no abnormal urination and defecation and abnormal body structure. The RD of the posterior bladder was measured through the abdominal wall in two groups of children by ultrasound. Results The average RD of the observation group was（34.14 ±7.11）mm（95%CI：33.05 ~ 35.22），and that of the control group was （23.74 ±8.84）mm（95%CI：22.41 ~ 25.07）. The average level of RD in the observation group was significantly higher than that in the control group（P < 0.05）. In the observation group，there was no significant difference in average RD between children with questionnaire and children without questionnaire. In the choice of treatment， there was no significant difference in the choice of final treatment between the diagnostic method of clinical interpre⁃ tation + BBD questionnaire + ultrasonic RD measurement and the diagnostic method of clinical interpretation + ultrasonic RD measurement only. Conclusion Transabdominal ultrasound RD measurement provides a more intuitive and accurate physical parameter for the diagnosis of BBD in children ，and has significant clinical application value. Clinical interpretation combined with ultrasonic RD measurement is a more accurate and simplified method for BBD diagnosis.