Objective To evaluate the value of early serum albumin(ALB) levels for predicting the prognosis of patients with severe traumatic brain injury(STBI). Methods A retrospective study was of 149 postoperative STBI patients who were aged over 18 and stayed over 7 days in the Intensive Care Unit of the Affiliated Hospital of Xuzhou Medical University from September 2015 to June 2020. Based on 28-day survival, the patients were divided into survival group and death group. Data were collected of the patient′s basic information, serum albumin levels at d 1,3, 5 and 7, and supplementary albumin volume at d 1-3, d 4-5, d 6-7. Multivariate logistic regression analysis was performed for independent risk factors affecting prognosis. Receiver operating characteristic (ROC) curve was drawn based on dynamic ALB levels and acute physiology and chronic health evaluation Ⅱ(APACHEⅡ)score to evaluate the predictive value for 28-day survival. The patients were grouped based on the ALB cut-off value at the corresponding time point, and Kaplan-Meier survival curve was used for analyzing the cumulative survival rate. Results Of 149 patients, 41 died in 28 days, with a fatality rate of 27.5%. With the prolonged treatment, the ALB level of the survival group showed a trend of gradual increase. The death group showed a decrease-increase trend of ALB levels, reaching the lowest at d 3. On d 3,5, and 7 of ICU stay, the ALB levels in the death group were significantly lower than that in the survival group [(35.22±0.54) vs (25.99±0.60), (36.58±0.54) vs (32.29±4.25), (36.70±0.49) vs (34.66±0.79) mmol/L, P＜0.05 for all). Analysis of the ROC curve showed that in predict-ing the 28-day death of patients with severe brain injury, the ALB levels at d 3 and d 5 of ICU stay had the highest value, and the area under the ROC curve (AUC) was 0.928 and 0.892 (both P＜0.001). APACHEⅡ score and the ALB level at d 7 of ICU stay were the second, and the AUC of the two were 0.801 and 0.616 (P＜0.05 for both). Using the ALB of 31.2 g/L at d 3 as the critical value for predicting 28-d death, it yielded a sensitivity of 95.12%, a specificity of 81.48%, a positive likelihood ratio of 3.02, and a negative likelihood ratio of 0.07. Analysis of the Kaplan-Meier survival curve showed that, at different time points in the ICU, the 28-d survivalrate of those above the cut-off value of ALB was significantly higher than that of those below, and the survival was longer. The 28-d survival rate was significantly higher in the patients with ALB＞31.2 g/L at d 3 than that of those with ALB≤31.2 g/L, and the survival was significantly prolonged [28-d survival rate:96.7% (89/92) vs 32.8% (19/57), χ²=68.068, P＜0.001; survival period (d):26.46 (23.96,30.11) vs 24.26 (19.93,28.46), Z=3.423, P=0.001]. Conclusion A decrease in ALB represents a poor prognosis for STBI patients, and the ALB level at d 3 in ICU has the highest prognostic value for those patients.