Objective:To explore the predictive value of C-reactive protein/albumin ratio (CAR) and systemic immune-inflammation index (SII) for opportunistic infection among acquired immune deficiency syndrome (AIDS) patients.Methods:From March 2020 to March 2022, a total of 220 AIDS patients treated in Honghu Center for Disease Control and Prevention were enrolled and they were divided into opportunistic infection group (178 cases) and non-infection group (42 cases) according to whether infection occurred; they were also assigned to bacterial infection group (22 cases), fungal infection group (63 cases) and mixed infection group (93 cases) according to different etiological characteristics. The general data were collected and CAR, SII were calculated according to laboratory indicators. Logistic regression was used to screen the risk factors affecting opportunistic infections or different etiological infections. The predictive value of CAR and SII on opportunistic infection and different etiological infections were compared by using receiver operating characteristic (ROC) curve.Results:The CD 4+T cell count, lymphocyte count were lower in the opportunistic infection group and the CRP, CAR, white blood cell count, neutrophil count, SII were higher in the opportunistic infection group compared with non-infection group, there were statistical differences ( P<0.05). The results of Logistic regression analysis showed that CAR and SII were the independent risk factors of opportunistic infection ( P<0.05). The area under the curve (AUC) of CAR to predict opportunistic infection was 0.886(95% CI 0.837 - 0.925), the specificity and sensitivity was 97.0% and 69.1%; the AUC of SII to predict opportunistic infection was 0.743(95% CI 0.680 - 0.799), the specificity and sensitivity was 52.4% and 88.2%. The results of Logistic regression analysis showed that CAR, monocyte count and SII were the independent risk factors for bacterial infection ( P<0.05). CAR and SII were the independent risk factors for fungal infection ( P<0.05). CD 4+ T cell count, CAR and SII were the independent risk factors for mixed infection ( P<0.05). The AUC of CAR to predict bacterial, fungal and mixed infection were 0.898(95% CI 0.797 - 0.960), 0.828(95% CI 0.742 - 0.895) and 0.923(95% CI 0.864 - 0.962), the optimum critical value were 0.49, 0.43, 0.40, the specificity were 98.7%, 95.2% and 92.9%, the sensitivity were 72.7%, 66.7% and 80.6%. The AUC of SII to predict bacterial, fungal and mixed infections were 0.627(95% CI 0.497 - 0.744), 0.782 (95% CI 0.633 - 0.811) and 0.780(95% CI 0.700 - 0.847), the optimum critical value were 385.13, 379.27, 390.10, the specificity were 55.4%, 52.4% and 54.8%, the sensitivity were 77.3%, 85.7% and 90.3%. Conclusions:CAR and SII can be used as predictors of AIDS opportunistic infection.