Abstract: DPOAE (distortion product otoacoustic emission) is a functional test of cochlear outer hair cells, which is a simple, non-invasive, sensitive and objective examination in audiological tests. In the occupational medicine area, combined with the pure tone test, it can be used for differential diagnosis of the pseudo deafness and exaggerated deafness, and to exclude the hearing damage caused by other factors. It is also useful to evaluate effectiveness of the treatment of deafness induced by occupational noise.