Objective To investigate the value of peripheral blood T-lymphocyte subsets and mitochondrial damage index(MDI)in evaluating the pregnancy outcome of patients with diminished ovarian reserve(DOR).Methods A total of 230 DOR patients admitted to the hospital from August 2020 to August 2023 were selected as DOR group,230 healthy women with normal ovarian reserve function were selected as control group,and all subjects were tested for peripheral blood T-lymphocyte subsets and MDI.DOR patients were di-vided into clinical pregnancy group(n=86)and non-clinical pregnancy group(m=144)according to clinical pregnancy.The influencing factors of pregnancy outcomes of DOR patients were analyzed by multivariate Lo-gistic regression model,and the predictive value of peripheral blood T-lymphocyte subsets and MDI for poor pregnancy outcomes of DOR patients was analyzed by receiver operating characteristic(ROC)curve.Results Com-pared with control group,CD3+,CD4+and CD4+/CD8+in DOR group were decreased(P＜0.05),and CD8+,positive rate of helper T cell(Th)-MDI and positive rate of suppressor T cell(Ts)-MDI were increased(P＜0.05).The clinical pregnancy rate of 230 DOR patients was 37.39％(86/230).Compared with clinical pregnancy group,CD4+in non-clinical pregnancy group was decreased(P＜0.05),and CD8+,CD4+/CD8+and the positive rates of Th-MDI and Ts-MDI were increased(P＜0.05).There was no significant difference in CD3+between two groups(P＞0.05).The levels of anti-Müllerian hormone(AMH)and estradiol(E2)in non-clinical pregnancy group were lower than those in clinical pregnancy group(P＜0.05).Th-MDI positive and Ts-MDI positive were independent risk factors for poor pregnancy outcomes in DOR patients(P＜0.05),and high levels of CD4+/CD8+,AMH and E2 were protective factors for poor pregnancy outcomes in DOR patients(P＜0.05).The area under the curve of AMH,E2,CD4+/CD8+,Th-MDI,Ts-MDI alone and com-bined in predicting poor pregnancy outcome in DOR patients were 0.735,0.784,0.767,0.691,0.703,0.882,respectively,and the predictive efficacy of combined application was significantly higher than that of each sin-gle application(P＜0.05).Conclusion DOR patients have immune dysfunction and oxidative activation,low CD4+/CD8+,Th-MDI positive and Ts-MDI positive are risk factors for poor pregnancy outcomes in DOR pa-tients,and the detection of the three has a high predictive effect on poor pregnancy outcomes in DOR patients.