Abstract: Objective To investigate the clinical efficacy of the levonorgestrel-releasing intrauterine system(LNG-IUS) combined with gonadotropin-releasing hormone agonist (GnRH-a) in the treatment of adenomyosis (AM) and to analyze the influencing factors for recurrence. Methods A total of 200 patients with AM admitted to the Department of Gynecology at Cangzhou People's Hospital from June 2022 to January 2024 were enrolled. They were divided into an intervention group and a control group using a random number table method, with 100 cases in each. The intervention group received LNG-IUS combined with GnRH-a, while the control group received GnRH-a alone. Clinical efficacy, menstrual blood loss assessed by Pictorial Blood Loss Assessment Chart (PBAC), dysmenorrhea severity evaluated by Visual Analogue Scale (VAS), sex hormone levels follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E₂), serum carbohydrate antigen 125 (CA125) levels, prostaglandin F₂α (PGF₂α) levels, adverse reactions, and recurrence were compared between groups. Multivariate logistic regression was used to analyze influencing factors associated with recurrence. Results The total effective rate was significantly higher, and the recurrence rate was significantly lower in the intervention group compared with the control group (P＜0.05). At 3 and 6 months after treatment, PBAC and VAS scores were significantly lower in the intervention group than in the control group (P＜0.05). After 6 months of treatment, levels of FSH, LH, E2, CA125, and PGF₂α were also significantly lower in the intervention group than in the control group (P＜0.05). Multivariate logistic regression analysis revealed that monotherapy regimen, FSH level＞15 IU·L^-1 at the end of treatment, and a reduction in CA125 ≤ 50% were risk factors for AM recurrence (P＜0.05). Conclusion The combination therapy of LNG-IUS and GnRH-a improves clinical efficacy and reduces recurrence risk in patients with AM. It exerts its therapeutic effects by alleviating menstrual blood loss, dysmenorrhea severity, and modulating relevant serological indicators. Monitoring FSH level and the extent of CA125 reduction at the end of treatment is essential to lower the likelihood of recurrence.