The principle of epileptic seizures is very complicated, simply put, it is an abnormal discharge of neurons in the brain, which is manifested as abnormal waves on the EEG. In most cases, the EEG is done in a normal state, so it is difficult to identify the cause and the “epileptogenic focus” of the patient, and the diagnosis can only be made after repeated and even induced epileptogenic examinations. The EEG is one of the most important clinical tests to confirm the diagnosis of epilepsy, so patients with epilepsy should not ignore the EEG. It has the following advantages: 1. It assists in diagnosis and typing: it is easier to diagnose patients with typical symptoms by doing EEG, and it takes several times or 24-hour video EEG monitoring examination to confirm the diagnosis in atypical patients. At the same time, doing EEG can exclude common seizure disorders in childhood such as syncope, childhood migraine and other seizure-like disorders. 2.Guidance on medication and evaluation of efficacy: When the epileptic patient is seizure-free after 2-3 years of standard medication, medication reduction can be considered, but the EEG must be rechecked several times before starting to gradually reduce the dosage. The key to surgical treatment is to locate the pre-epileptic focus with advanced EEG. In general, 24-hour video EEG monitoring is recommended for the first diagnosis of the child. Long-range EEG monitoring can improve the positive rate and exclude other seizure disorders, which is very useful for diagnosis and differential diagnosis. EEG is reviewed at 3 months of treatment, and later it is recommended to review EEG every 6 months.