Abstract: OBJECTIVE To observe the association of vaginal microecological characteristics with imbalance of type 1 helper T cells (Th1) /type 2 helper T cells (Th2) of the human immunodeficiency virus (HIV) infection patients complicated with cervical cancer and cervical intraepithelial neoplasia (CIN) and explore the impact of vaginal microecological characteristics on HIV infection and cervical carcinogenesis. METHODS Totally 160 patients with cervical cancer and CIN who were treated in Beijing Ditan Hospital, Capital Medical University form Aug. 2015 to Aug. 2025 were recruited as the research subjects. A regular HIV infection test was carried out. The enrolled patients were divided into the group A with 31 cases (HIV + cervical cancer), the group B with 37 cases (HIV + CIN), the group C with 25 cases (HIV-cervical cancer) and the group D with 67 cases (HIV-CIN). Univariate analysis and multivariate logistic regression analysis were performed for the influencing factors for cervical cancer. The mediating effect of the vaginal microecological characteristics on HIV infection and cervical carcinogenesis was detected by means of Bootstrap. RESULTS The Th1, Th1/Th2, interferon-γ(IFN-γ) and interleukin-2(IL-2)were lower in the group A and the group B than in the group C and the group D; the Th2, IL-4 and IL-10 were higher in the group A and the group B than in the group C and the group D(P＜0.05). The Th1, Th1/Th2, IFN-γ and IL-2 of the patients with abnormal vaginal microecology were lower in the HIV-positive patients than in the HIV-negative patients; the Th2, IL-4 and IL-10 were higher in the HIV-positive patients than in the HIV-negative patients (P＜0.05). The number of sexual partners (more than 3), genotypes of HPV infections(HPV16/18), positive test of HIV and abnormal Lactobacillus were the risk factors for the cervical cancer, and the age of first sextual intercourse was a protective factor(P＜0.05). The positive test of HIV has direct impact on the cervical lesions, and the abnormal Lactobacillus partly mediated the impact of positive HIV test on the cervical carcinogenesis(P＜0.05). CONCLUSIONS The HIV infection can result in the abnormal vaginal microecology and imbalance of Th1/Th2 in the patients with cervical lesions. The abnormal vaginal microecology was associated with the imbalance of Th1/Th2. The abnormal Lactobacillus partly mediates the impact of positive HIV test on the cervical carcinogenesis.