1) conductive deafness: it can occur in the lesions of external auditory canal, tympanic membrane, middle ear or eustachian tube. Such as cerumen embolism, tympanic membrane perforation, tympanic effusion and otosclerosis.

(2) The lesion of sensorineural deafness is located in the inner ear, auditory nerve or auditory conduction pathway. Such as inner ear hypoplasia, drug-induced deafness, noise deafness and acoustic neuroma.

(3) Mixed deafness: both conductive deafness and sensorineural deafness.

(4) Central deafness: It can occur anywhere in the central nervous system from his nucleus to the cerebral cortex.