OBJECTIVE The purpose of this meta-analysis was to assess the diagnosis and prognostic value of plasma copeptin levels after traumatic brain injury (TBI). METHODS The databases PubMed, Cochrane Library, OvidSP, Google Scholar, VIP, CNKI, and WFSD were systematically searched from the inception dates to May 9, 2020. The pooled analysis of relevant data was conducted by the RevMan 5.3 software. Subgroups analysis was performed to explore the impact of age, country, male ratio, follow-up time, and Glasgow coma score (GCS) on the pooled area under curve (AUC) values of assessment mortality. RESULTS A total of 17 studies involving 2654 participants were included in the current meta-analysis. The pooled results demonstrated that increased plasma copeptin levels were significantly associated with TBI [SMD, 2.44; 95%CI, 1.59 ~ 3.29; P < 0.00001] and also were significantly associated with mortality [SMD, 1.37; 95%CI, 1.16 ~ 1.58; P < 0.00001], and poor functional outcomes (PFO) [SMD, 1.44; 95%CI, 1.20 ~ 1.68; P < 0.00001] in patients with TBI. Furthermore, the copeptin had a significant value in diagnosing brain concussion [AUC, 0.90; 95%CI, 0.84 ~ 0.95; P < 0.00001] and predicting progressive hemorrhagic injury [AUC, 0.83; 95%CI, 0.80 ~ 0.87; P < 0.00001], acute traumatic coagulopathy [AUC, 0.84; 95%CI, 0.79 ~ 0.89; P < 0.00001], mortality [AUC, 0.89; 95%CI, 0.87 ~ 0.92; P < 0.00001], and PFO [AUC, 0.88; 95%CI, 0.84 ~ 0.92; P < 0.00001] in patients with TBI. The subgroup analysis findings suggested that the age, country, male ratio, follow-up time, and GCS were not obvious factors influencing the pooled AUC values of assessment mortality. CONCLUSIONS The authors indicate that the plasma copeptin is a potentially promising biomarker for TBI diagnosis and prognosis prediction.