Functional epilepsy refers to epileptic foci located in functional areas, such as motor cortex, sensory cortex, visual cortex, and language cortex. Surgical removal of epileptic foci in these areas will result in postoperative language dysfunction (aphasia, unfavorable speech, inability to understand others), motor-sensory dysfunction (limb weakness, hemiparesis, limb sensory numbness), and visual dysfunction (visual field defects). For epilepsy involving functional areas, it has been a more difficult problem for epilepsy surgery because of the contradiction between functional preservation and epilepsy control. Therefore, defining the functional area and pinpointing the epileptogenic focus is the key to functional epilepsy surgical treatment. Currently, intracranial electrodes are considered the gold standard for localizing epileptic foci, while direct cortical electrical stimulation is the gold standard for localizing functional areas of the cerebral cortex. EEG is still the most important reference indicator for surgical treatment of epilepsy, but conventional scalp EEG is affected by a variety of activities such as scalp, cranial, electromyographic activity and motor artifacts, which produce attenuation of EEG wave amplitude; or the number of synchronously active nerve cells alters the EEG waveform, reducing the detection rate of epileptic waves. Scalp electrodes require at least 6 cm of synchronized neuronal discharges to record abnormalities, while intracranial electrodes can directly record EEG activity in the cerebral cortex and internal brain tissue, and can detect abnormal cortical discharges within 1 cm, with the advantages of clear graphics and high sensitivity. For those cases where the epileptogenic focus cannot be clearly identified by noninvasive examination, intracranial electrode EEG monitoring is a safe and reliable localization method. Currently, in most foreign epilepsy centers, intracranial electrodes are still used in 25-40% of epilepsy surgical patients despite the development of non-invasive affective techniques.