To study the damage to the hearing of miners under the shaft caused by noise and its recovery, an experiment with imitated noise was carried out in guinea pigs. The animals were divided into five groups with exposure to imitated underground noise of 117 dB (A) for one hour for one, two, four, eight and 16 days, respectively, and one control. Thresholds of cortex reaction and evoked electric reaction of brain stem were detected before and after exposure. And, ultrastructural changes in cochlear hair cells were observed by scanning and transmission electron microscopy. Results showed that exposed noise level and length since removing from exposure had significant effects on changes in hearing threshold. Damage to hearing was aggravated with prolonged exposure, to various extent, from changes in temporary threshold shift and permanent threshold shift to recovery from it after removing from exposure. Intracellular structural changes in internal and external hair cells and their injury deteriorated gradually with increase of exposure levels, at worst, to changes in epithelial plate, collapse of Corti's organ and vacuolation, edema and degeneration of cells. It suggests it is important to protect workers form exposure to noise.