Abstract: OBJECTIVE To explore the expression of monocyte HLA-DR and Th17/Treg cytokines in patients with secondary infection after severe trauma and analyze its clinical value. METHODS Totally 96 patients with severe trauma admitted to the Second Affiliated Hospital of Xi’an Medical College from Mar. 2017 to Dec. 2018 were selected as srudy subjects, and were divided into 39 patients of infection group and 57 patients of non-infection group according to whether secondary infection occurred. Human leukocyte antigen-DR（HLA-DR） expression in monocytes were determined, interleukin-17（Interleukin, IL-17）, interleukin-10（Interleukin, IL-10） and interferon gamma（ Interferon-γ, IFN-γ） in peripheral blood were detected, and mRNA expression of orphan nuclear receptor（RORγt） mRNA and forkhead pterygnet transcription factor（Foxp3）were detected by RT-PCR. RESULTS The expression of HLA-DR in the infection group was（37.18±4.52）%, significantly lower than that in the non-infection group（P＜0.001）. The expressions of Th17, Treg and Th17/Treg in the infection group were（1.63±0.32%）,（4.10±0.63）%, and（0.40±0.08）, respectively, significantly higher than those in the non-infection group（P＜0.001）. IL-17 and IL-10 in the infection group were（32.42±8.73）pg/L and（35.46±6.87）pg/L, respectively, significantly higher than those in the non-infection group, while IFN-γ was（314.24±49.98）pg/L, significantly lower than that in the non-infection group（P＜0.001）. The mRNA levels of Foxp3 and RORγt in the infection group were（3.26±0.82） and（4.71±0.89）, respectively, significantly higher than those in the non-infection group（P＜0.001）. CONCLUSION The levels of HLA-DR and Th17/Treg cytokines in monocytes had important predictive value for patients with secondary infection after severe trauma and had certain clinical research value.