EEG is a graph obtained by magnifying and recording the spontaneous bio-potentials of the brain on the scalp with a sophisticated electronic instrument, which records the spontaneous, rhythmic electrical activity of groups of brain cells through electrodes. It is performed by attaching a special sensor of electrodes to the patient’s head, and the computer records the electrical activity of the patient’s brain on a screen or on paper in the form of a wave-like curve. EEG is a common ancillary test used in neurology to check for abnormalities in brain waves for many types of diseases, such as various types of epilepsy, central nervous system infections, vascular headaches, and cerebrovascular disease. Under normal conditions, there is a fixed rhythm of brain waves. If spike, spike, spike-slow integrated wave, spike-slow integrated wave, or multiple spike-slow integrated waves are present, it indicates the presence of seizures and is the most important auxiliary test to confirm the diagnosis of epilepsy. In cases of parenchymal brain injury, such as various types of encephalitis, diffuse EEG abnormalities can also occur, and although there are no epileptic waves, they can be used as indirect evidence of parenchymal brain injury. Abnormal EEG can only indicate a functional state of the brain, and has definite diagnostic significance after comparing and observing the clinical symptoms of the patient before and after the examination, and combining with other auxiliary examinations.