A cochlear implant is an electronic device that replaces the function of the human ear and helps adults and children who are severely or profoundly deaf to restore or provide the sense of hearing and improve their ability to communicate with others. The cochlear implant consists of electrodes and receivers implanted in the body, and a speech processor, microphone and transmitter outside the body. Sound is received by the microphone and converted into an electrical signal and transmitted to the speech processor, which amplifies and filters the signal and transmits it from the transmitter to the receiver, where it generates electrical impulses that are transmitted to the corresponding electrodes, causing excitation of the auditory nerve fibers and transmitting sound information to the brain, resulting in hearing. As some patients with severe or very severe sensory hearing loss is more serious, the average hearing threshold of speech frequency is often more than 90 decibels, even after the amplified sound is difficult to hear, the effect of wearing hearing aids is poor. This is because inner ear diseases, drug intoxication or other causes of damage to the sensory cells of the inner ear severely impede the transmission of auditory information, and the patient’s central auditory system cannot receive sufficient information despite the natural and clear sound amplified from the outside world. Cochlear implants can bypass the damaged structures in the inner ear and directly stimulate the auditory nerve, allowing patients to regain their hearing. Cochlear implants can help people who are severely or profoundly deaf communicate better with others, thereby allowing them to have more educational and employment opportunities and to return to mainstream society. In Europe and the United States, the indications for cochlear implants have been relaxed to 75 decibels or higher. With the continuous improvement of cochlear implant technology, unilateral deafness has been proven to have the same hearing effect as the normal ear, and Europe and the United States have included unilateral deafness in the indications for cochlear implants. The cochlear implant is also available for some developmental malformations such as MONDINI malformation. The development trend of cochlear implants is the continuous improvement of technology, the miniaturization and aesthetics of in vitro machines, and bilateral cochlear implants are the future trend.