Objective: To evaluate the efficacy and prognosis of loop cutaneous ureterostomy (LCU) in the treatment of primary obstructive megaureter (POM) with severe hydroureteronephrosis (HUN) in infants under 1 year of age，so as to provide reference for infants unsuitable for stage-Ⅰ ureteral reimplantation. Methods: A retrospective analysis was conducted on 12 infants with POM and severe HUN treated with LCU in our hospital during Jan.2019 and Dec.2023.The clinical characteristics，surgical techniques，indications，postoperative complications，stage-Ⅱ surgical approaches，and follow-up outcomes were summarized. Results: All operations were successful，with an average operation time of (37.08±7.53) min (6 left-sided LCU and 6 right-sided LCU).During the mean follow-up of (10.12±2.70) months，all infants showed clinical improvement，with complete resolution or significant alleviation of hydronephrosis，reduced ureteral diameter，and increased renal cortical thickness.Complications included asymptomatic bacteriuria in 3 cases (25%) and urinary tract infection (UTI) in 1 case，all resolved with oral antibiotics.Four cases developed peristomal rashes，which improved with topical treatment.Eleven infants underwent stage-Ⅱ Cohen ureterovesical reimplantation at a mean age of (15.20±2.07) months.Notably，27.3%(3/11) required ureteral tailoring or plication during reimplantation，which reduced the risk of ischemic necrosis from excessive trimming.During the follow-up of (22.17±13.93) months，hydronephrosis and renal function improved，and no febrile UTI or bladder dysfunction occurred. Conclusion: LCU is a safe and effective method，which can provide adequate urinary drainage，relieve obstruction，stabilize renal function，and allow time for ureteral maturation and renal parenchymal recovery.LCU also facilitates subsequent stage-Ⅱ surgery by reducing ureteral dilation.