To investigate the effects of hematocrit (Hct) on short-term prognosis in severe traumatic brain injury patients after undergoing decompressive craniectomy and the influencing factors of Hct. Methods： We retrospectively included in this study 155 severe head injury patients who underwent unilateral decompressive craniectomy in our hospital and collected information such as their age, gender, and test results before and after the operation. Univariate and multivariate logistic regression was applied to analyze the impact that post-surgery Hct and other factors have on short-term mortality one month after surgery. Multiple linear regression was used to study the influencing factors of Hct after surgery. The receiver operating characteristic (ROC) curve for Hct and short-term prognosis was described. Results：The short-term mortality of severe traumatic brain injury patients after undergoing decompressive craniectomy was 29.03% (45/155). Multivariate logistic regression analysis showed that age (OR=1.043), GCS score upon admission (OR=0.716), ISS score (OR=1.126), and Hct after surgery (OR=0.925) were the independent risk factors of short-term patient mortality after decompressive craniectomy. Multiple linear regression showed that GCS score upon admission (β=0.299), Hct before surgery (β=0.480), and volume of colloidal fluid infusion during surgery (β=-0.004) were independent influencing factors of post-surgery Hct. From the ROC curve, we found that the best critical value of post-surgery Hct was 25% (YI=0.225) and its sensitivity and specificity were respectively 73.6% and 48.9%; greater than this, the short-term patient survival rate was 79.5%. Conclusion：The Hct after decompressive craniectomy in severe traumatic brain injury patients is a risk factor for short-term survival. Having a post-surgery Hct no less than 25% may result in a higher short-term patient survival rate. Patients with a higher GCS score upon admission and a higher Hct before surgery or those with a smaller colloidal fluid infusion during surgery may experience less Hct decrease after surgery.