Objective To conduct a comprehensive quantitative evaluation of the primary lesions and secondary damages of the inner ear in the rat model of intratympanic injection of gentamicin. Methods Sixteen adult rats were randomly divided into four groups, 4 rats in each group: normal control group (8 ears), 7 days after single intratympanic injection of gentamicin (40 mg/ml) (8 ears), 30 days after single injection of gentamicin (8 ears), and 60 days after single injection of gentamicin (8 ears). One ear of the tested rats was made into flat surface preparations of whole membranous labyrinth to quantitatively evaluate the hair cell density in each sensory epithelial region, and the other ear was made into temporal bone sagittal slices to quantitatively evaluate the density of cochlear and vestibular neurons and the density of their peripheral and central nerve fibers. Results Quantitative analysis of hair cells in the surface preparations of whole membranous labyrinth showed that the range and degree of hair cell damage at different times after intratympanic injection of gentamicin were basically the same, indicating that the one-time destruction of hair cells by intratympanic injection of gentamicin did not cause obvious secondary degeneration to surviving hair cells. Quantitative analysis of the inner ear nervous system in sagittal sections of the temporal bones showed that as time passed after tympanic administration of gentamicin, the peripheral nerve fibers of the cochlear and vestibular neurons had disappeared 30 days after the death of the hair cells, but the soma of the inner ear neurons and their central nerve fibers had not yet developed lesions 30 days after the death of the hair cells. It was not until 60 days after the death of the hair cells that the inner ear neurons and their central nerve fibers showed obvious secondary damage. Conclusion The degeneration of the peripheral nerve fibers of inner ear neurons after the loss of hair cells is not synchronized with the delayed destruction of inner ear neurons and their central nerve fibers. The early degeneration of peripheral nerve fibers can only indicate whether the neural connection between inner ear neurons and inner ear sensory epithelium has been completely lost, and the secondary destruction of central nerve fibers can prove whether the neural connection between the inner ear and the central nervous system is completely interrupted.