Aim:Lower admission systolic blood pressure (SBP) in patients with severe traumatic brain injury (sTBI) is closely linked to mortality. However, research on the function of serum lactate (Lac) and other hemodynamic parameters including diastolic blood pressure (DBP) and mean arterial pressure (MAP) performed in the acute-phase mortality of sTBI patients is quite limited. This study was designed to explore theses complex interrelationships.Material and Methods:Clinical data for sTBI (Glasgow Coma Scale (GCS)≤8 on admission) was collected from different hospitals for the period 2013 to 2024. One-week mortality was the endpoint. The associations of all blood pressure (BP) indices and Lac with one-week mortality were investigated using mixed effects logistic regression models and the diagnostic potency of mortality analysis based on Lac was presented through receiver operating characteristic curve (ROC) and area under curve (AUC). In addition, the relationships between BP indices and Lac were assessed using linear regression analysis.Results:A total of 1270 sTBI patients were analysed for this study. Smooth u-shaped associations of different admission BP indices with one-week mortality were demonstrated through bivariate analysis and the extreme values in BP indices were found to be associated with increased mortality, no obvious threshold effect being revealed. After adjustments were made for confounding factors, the likelihood of death was obviously increased with a SBP<100 mmHg, a DBP<70 mmHg, a MAP<80 mmHg and a Lac>4.5. Furthermore, all three BP indices were significantly negative with Lac. Meanwhile, MAP has the strongest ability to predict one-week mortality in sTBI patients, and it also has the strongest negative correlation with Lac.Conclusion:It is advised that guidelines for the management of sTBI patients should reconsider the definition of hypotension and use all three BP indices and serum Lac as references instead of a single hypotension at SBP<90 mmHg for improving survival rate.