Radiation-induced brain injury is a common complication after radiotherapy for head and neck tumors. It can occur at any time after radiotherapy. The common sites are closely related to the radiotherapy regimen and are more frequently seen in areas receiving the highest radiotherapy dose. Early symptoms include fatigue, dizziness and headaches. In the later stage, epileptic seizures, personality changes and progressive decline in neurocognitive function may occur. Brain computed tomography (CT) often shows focal low-density images, and brain magnetic resonance imaging (MRI) presents with “finger-like” edema in the white matter of the brain during the edema stage. The use of multimodal MRI, positron emission tomography (PET) and other imaging techniques can help to make early diagnosis and differential diagnosis of radiation-induced brain injury. The treatment options include medication, hyperbaric oxygen therapy, surgery and mesenchymal stem cell transplantation. Commonly used drugs in clinical practice include bevacizumab, dexamethasone, citicoline and gangliosides. With the increasing attention paid to radiation-induced brain injury, the research on related mechanisms has been continuously deepened and the corresponding therapeutic drugs have achieved good therapeutic effects. However, effective prevention is more important than treatment. As the brain has complicated structure and functions, damage to functional areas can lead to disability or even death. Optimizing radiotherapy techniques can achieve precise irradiation of tumors and reduce the volume of normal brain tissue exposed to radiation. Radiotherapy plans should be formulated based on factors such as the patient’s age, underlying diseases, and tumor location to avoid excessive exposure to radiation-sensitive areas. Using hippocampal protective radiotherapy to reduce the radiation dose to the hippocampal region can significantly decrease the risk of memory decline and allow the reasonable control of the radiotherapy. The diagnosis and treatment of radiation-induced brain injury is a multidisciplinary collaborative process. It is necessary to strengthen the full life cycle management of patients with head and neck tumors undergoing radiotherapy. Through technological innovation and individualized treatment, the incidence and harm of brain injury should be further reduced.