Objective To explore the clinical characteristics and related factors of mental disorder caused by brain injury in the judicial identiifcation of mental illness. Methods Forensic case data of brain injury ware collected and analized. Brain injury sverity was classied into 3 groups, namely severe group(group A); moderate group (group B) and mild group(group C) according to neurosurgery GCS scores; clinical characteristics were analyzed, diagnosis were made against the Chinese Classiifcation of Mental Disorders (the 3rd ed.) (CCMD-3). Relationship between the clinical characteristics and brain damage severity was analyzed. Results Organic neurosis-like syndromes are the main manifestation of mental disorders caused by mild and moderate brain injuries. Organic intellectual deifciency is the main manifestation of mental disorders due to severe brain injury. The difference between the three groups was significant (P ≤ 0.01). Conclusion Different clinical features are related to different brain injury severities in the forensic evaluation of mental disability.