Cochlear implantation can be chosen for those with severe or profound deafness in both ears, with the lesion site localized and diagnosed in the cochlea. Selection criteria for patients with prelingual deafness: (1) Severe or profound sensorineural deafness in both ears. (2) The optimal age should be 12 months to 5 years old. before 2 years old is the best. (3) Appropriate hearing aids and no significant improvement in hearing and speech after 3 to 6 months of hearing rehabilitation. (4) No contraindication to surgery. (5) The family and/or the implantee himself/herself have a correct understanding of cochlear implants and appropriate expectations. (6) There are conditions for hearing and speech rehabilitation education. The younger the patient is at the time of surgical implantation, the better the outcome, which maximizes the potential for avoiding auditory sensory deprivation and expanding speech and language skills before the critical period of brain plasticity. Children or adolescents older than 6 years of age need to have some foundation in hearing and speech, a history of hearing aid wear and a history of hearing or speech training since childhood. Ineffective or very ineffective hearing aids are defined as ≤30% open phrase recognition or ≤70% two-word word recognition in the best hearing aid listening environment. 2. Selection criteria for postlingually deaf patients: (1) Postlingually deaf patients of all ages. (2) Severe or profound sensorineural deafness in both ears. (3) Hearing aid is ineffective or very ineffective, and the recognition rate of open phrases is ≤30%. (4) No contraindication to surgery. (5) Have good psychological quality and subjective initiative, correct understanding of cochlear implants and appropriate expectations. (6) Have family support. The age of onset and duration of deafness in patients with postlingual deafness are closely related to the outcome after surgery. Generally speaking, those with early age of onset and longer duration of deafness have poorer results after surgery. In addition, the listening environment in life and work after surgery can also affect the effect of cochlear implantation. Contraindications to surgery: (1) Absolute contraindications, including cases of severe malformations of the inner ear, such as Micheal’s malformation, cochlea-less malformation, and so on. Auditory nerve defects. Severe mental retardation. Inability to cooperate with speech training. Severe mental illness. Those with acute or chronic inflammation of the middle ear mastoid that has not been cleared. (2) Relative contraindications, including poor general condition. Uncontrollable epilepsy. No reliable conditions for rehabilitation training. Secretory otitis media and glue ear are not contraindications to surgery. Chronic otitis media with tympanic membrane perforation can be selected for one-stage or staged surgery if the inflammation is controlled. One-stage surgery refers to radical treatment of the mastoid lesion, tympanic membrane repair (or mastoid cavity temporalis muscle tamponade and closure of the external auditory canal) and cochlear implantation at the same time. Staged surgery refers to the removal of the lesion, repair of the tympanic membrane perforation or closure of the external auditory canal, followed by cochlear implantation after 3 to 6 months.