EEG has certain diagnostic value for brain diseases, but it is limited by many conditions, so it cannot be the only basis for diagnosis in most cases, but needs to be analyzed comprehensively with the patient’s symptoms, signs, other experimental tests or auxiliary tests. EEG is mainly used for the examination of intracranial organic lesions such as epilepsy, encephalitis, cerebrovascular disease and intracranial space-occupying lesions. EEG is highly susceptible to interference by various factors, and care should be taken to recognize and exclude them. Purpose of examination Epilepsy: EEG has the greatest value in the diagnosis of epilepsy, and can help to determine the diagnosis and staging, judge the prognosis and analyze the efficacy of treatment;