Deafness has become one of the most common chronic diseases in modern society and should be given our full attention. Deafness can be classified according to the nature of the lesion: (1) Conductive deafness: Any structural or functional disorder occurring in the outer ear, middle ear or inner ear sound conduction pathway can cause conductive deafness. In conductive deafness, the air-conduction hearing loss is usually no more than 60 dB, while the bone conduction hearing is basically in the normal range. (2) Sensorineural deafness: Due to damage to the hair cells of Corti, auditory nerve, auditory transmission pathway or hearing centers at all levels, resulting in impairment of sound sensation or nerve impulse transmission, it is called sensorineural deafness, in which both air and bone conduction hearing is reduced. In this case, the damage to the hair cells caused by noise, infection, ototoxic drugs and genetic factors is called sensorineural deafness (cochlear deafness), which often has the phenomenon of resonance. If the lesion is located in the auditory nerve and its conduction pathway, it is called neurological deafness and central deafness (collectively called postcochlear deafness), such as auditory neuroma and auditory neuropathy, etc. The speech recognition rate is often significantly decreased, and the patient complains that he can hear the sound but cannot distinguish its meaning. (3) Mixed deafness: those with both conductive deafness and sensorineural deafness caused by lesions in the external ear and/or middle ear, as well as lesions in the hair cells of the Corti apparatus or the auditory nerve are called mixed deafness, such as otosclerosis with simultaneous involvement of the auditory chain he cochlea, temporal bone mixed har fracture, chronic suppurative otitis media, cholesteatoma, middle ear tumor, etc. 2. functional deafness; 3. pseudo-deafness. The World Health Organization (WHO) in 1997 classified hearing loss into the following grades according to the average threshold of air conduction at 500Hz, 1000Hz, 2000Hz and 4000Hz: 1) mild hearing loss: 26-40dBHL; 2) moderate hearing loss: 41-55dBHL; 3) moderate to severe hearing loss: 56-70dBHL; 4) severe hearing loss: 71-70dBHL; 5) hearing loss: 71-70dBHL. 1.Severe hearing loss: 71-90dBHL; 5.Extreme hearing loss: ≥91dBHL. 3.Common methods to assess the cause of deafness and lesion site 1.Pure tone hearing threshold test (directional condition response test): pure tone hearing threshold test responds to the hearing sensitivity of the subject ear to pure tones of various frequencies and estimates the degree of auditory damage. The general pure-tone hearing threshold test is suitable for adults, children over 12 years old, and children over 6 months old for directional conditioned reflex testing (visual reinforcement audiometry or conditioned play audiometry). 2. Acoustic conductance test: Acoustic conductance test is an objective test of the middle ear conduction system, inner ear function, auditory nerve, and brainstem auditory pathway function, and is suitable for all types of people. Generally speaking, the curve is type A for any person with normal middle ear function; type As is commonly seen when the middle ear conduction system activity is restricted such as ear cherry, fixed auditory chain or obvious thickening of the tympanic membrane; if its activity is increased, such as interruption of the auditory chain, atrophy of the tympanic membrane, healing perforation and abnormal opening of the eustachian tube, the curve can be Ad; type B curve is mostly seen in those with fluid in the tympanic chamber and obvious adhesions in the middle ear; type C curve indicates eustachian tube C curve indicates dysfunction of the eustachian tube and negative pressure in the tympanic chamber. 3.Auditory brainstem response audiometry (ABR): divided into auditory brainstem response threshold and auditory brainstem response latency, ABR refers to the detection of brainstem bioelectric response induced by acoustic stimulation, ABR can be used to determine high frequency hearing threshold, neonatal and infant hearing screening, identification of organic and functional deafness, diagnosis of small horn occupational lesions in the brain, etc. 4.Aberrant otoacoustic emissions: It is an objective auditory function test that depends on the integrity of the overall cochlear function and is closely related to the function of the outer hair cells of the cochlea. 5.40Hz auditory correlation potential: It is an auditory steady-state evoked potential, which is a kind of medium latency response. It is mainly used for objective assessment of hearing threshold thresholds, and is especially valuable for determining hearing thresholds at frequencies below 1000 Hz. It can help to understand the low frequency of newborn hearing screening and ABR response in those who are not elicited. 6, steady-state auditory evoked potentials (ASSR): there is a continuous or steady-state sound stimulus signal evoked by the generation of brain electrical response. ASSR belongs to the objective listening method, can detect each frequency threshold, in the inability to conduct behavioral audiometry or behavioral audiometry can not get satisfactory results in the audiometry of people (especially ≤ 6 months of age infants and children), is very important. 7. Speech recognition rate: The percentage of words that the subject ear can understand in the measured vocabulary. Combined with audiological assessment it can be used to determine the type of deafness at first glance. 8. Newborn hearing screening: Newborns receive auditory brainstem response or otoacoustic emission screening within 6-48 hours after birth, and if they do not pass the screening within one month, the diagnosis is confirmed within three months and intervention is performed before 6 months of age.