Abstract: Objective To detect the dynamic serum cortisol level and evaluate its clinical significance in the patients with traumatic brain injury(TBI). Methods Total 60 cases of traumatic brain injury in our hospital from January, 2016 to June, 2016 were included, and were classified into three groups according to the Glasgow Coma Scale(GCS):mild, moderate(GCS 13-15) and severe group(GCS 9-12) after admittance(GCS 3-8). The blood sample of those patients were collected in the morning 8 am on 1 d, 3 d, 7 d, 14 d, and 6 months later; the level of serum cortisol was tested by using chemiluminescence immunoassay. Results The serum cortisol concentrations in patients with mild and moderate groups were in the normal range, and the change range was small, while the severe group had the greatest degree of variation(F=11.325, P<0.01). The change of the serum cortisol concentration of the patients in the first 1 week was the largest, and then gradually became normal. The number of patients with normal cortisol, rising or falling levels of cortisol were 28 cases, 26 cases and 6 cases, respectively. According to the definition of the prognosis, there were 11 patients with poor prognosis, 49 patients with good prognosis. The good rate was 87% in the normal and ascending group of cortisol concentration, which was significantly higher than that in the lower cortisol group(33.3%), which indicated that the lower the concentration, the worse the prognosis. Conclusion The cortisol levels changed more significantly with the severity of TBI, and the patients with low serum cortisol level usually had poor outcomes.