Objective:To explore the influencing factors for poor prognosis in patients with severe traumatic brain injury (TBI).Methods:A retrospective analysis was performed; the clinical data of 389 patients with severe TBI admitted to Department of Neurosurgery, 900 th Hospital of PLA Joint Logistics Team from January 2018 to December 2022 were collected. Glasgow Outcome Scale (GOS) was used to evaluate the prognoses 6 months after discharge. Differences in clinical data between the good prognosis group (GOS scores of 4-5) and poor prognosis group (GOS scores of 1-3) were compared. Multivariate Logistic regression was used to analyze the independent influencing factors for poor prognosis in severe TBI patients, and receiver operating characteristic (ROC) curve was used to analyze the predictive value of the regression model in severe TBI patients. Results:At 6 months after discharge, 182 patients (46.8%) had favorable prognosis and 207 patients (53.2%) had unfavorable prognosis. Compared with the good prognosis group, the poor prognosis group had significantly older age, lower Glasgow Coma Scale (GCS) scores, higher proportions of patients with subdural hematoma (SDH), cerebral hernia, cerebral infarction and encephalocele, higher blood glucose, lower albumin, lower K +, Ca 2+ and CO 2, higher international normalized ratio (INR) and C-reactive protein (CRP), lower lymphocyte/monocyte ratio (LMR), and higher neutrophil/lymphocyte ratio (NLR) and systemic immunoinflammatory index (SII, P<0.05). Multivariate Logistic regression analysis showed that age ( OR=1.045, 95% CI: 1.025-1.066, P<0.001), GCS score ( OR=0.487, 95% CI: 0.388-0.612, P<0.001), cerebral hernia ( OR=3.471, 95% CI: 1.604-7.511, P=0.002), blood glucose ( OR=1.109, 95% CI: 1.010-1.218, P=0.030), INR ( OR=8.073, 95% CI: 1.199-54.354, P=0.032) and high SII ( OR=8.311, 95% CI: 4.089-16.892, P<0.001) were independent influencing factors for poor prognosis in severe TBI patients. ROC curve showed that area under the curve of the regression model predicting poor prognosis in severe TBI patients was 0.935 (95% CI: 0.905-0.957, P<0.001), enjoying sensitivity of 88.89% and specificity of 85.16%. Conclusion:Severe TBI patients with advanced age, low GCS score, high INR and SII, elevated blood glucose, or cerebral hernia have poor prognosis.