To explore the curative effect of gonadotropin-releasing hormone agonist (GnRH-a) combined with levonorgestrel releasing-intrauterine systems (LNG-IUS) for treating patients with abnormal uterine bleeding caused by diffuse adenomyosis (AUB). Methods: A total of 120 patients with AUB who treated in obstetrics and gynecology clinic were selected and were randomly divided into two groups (60 cases in each group) between June 2019 and July 2021. The patients in the study group were treated with GnRH-a combined with LNG-IUS, and the patients in the control group were treated with oral contraceptives (COC) combined with LNG-IUS. The efficacy of the treatment, and the changes of menstrual blood volume score by pictorial blood loss assessment chart (PBAC), the uterine volume size, and levels of serum CA125 and hemoglobin (Hb) before and after treatment of the patients were compared between the two groups. Results: The symptom improvement rate (98.3%) and the Hb level (109.57±7.31g/L) of the patients in the study group after treatment were significantly higher than those (85.0% and 105.03±8.39g/L) of the patients in the control group. The vaginal irregular bleeding rate (5.0%), the rate downward displacement of LNG-IUS (0), the uterine volume (101.93±4.40cm3), the serum CA125 level (12.34±2.71U/ml), and the PBAC score (25.95±3.64 points) of the patients in the study group after treatment were all significantly lower than those in control group (35.0%, 10.0%, 178.16±6.97cm3, 19.11±3.83U/ml, and 45.63±5.97 points) of the patients in the control group (all P＜0.05). Conclusion: GnRH-a combined with LNG-IUS for treating patients with abnormal uterine bleeding caused by diffuse AUB can increase the clinical efficacy, and which can significantly improve the menstrual volume, with less influence on the downward displacement of LNG-IUS.