Interpretation of cochlear active acoustic amplification mechanism has always been unsolved medical problems. This mechanism is closely related to the motion of the stereocilia at the top of the outer hair cells in the cochlea. The stereocilia motion is regulated by the tip-link tension and the fluid force of the lymph fluid. Therefore, studying the tip-link tension during the stereocilia motion is an important part of the interpretation of the cochlea's active sensory sound amplification mechanism. Most previous studies regard stereocilia as rigid bodies, and ignore the influence of shaft bending when studying the mechanical properties of hair bundle. Most researches on elastic stereocilia use finite element simulation, or simplify the model by ignoring the fluid-solid coupling with lymph fluid, or only consider static loading. Based on the Poiseuille flow combined with the distributed parameter model, the analytical solution of the elastic stereocilia motion is derived in this paper. The dynamic response of the stereocilia under the shear force of the tectorial membrane and the change law of tip-link tension were studied. Shaft bending produces a nonlinear accumulation of displacement at the height of the stereocilia. The higher the stereocilia, the more obvious this accumulation effect is. Under the action of dynamic load, the shaft bending contributes the most to the displacement response in the tall stereocilium, and this contribution is easily affected by frequency changes. Under low frequency load, the displacement response of tall stereocilium mainly comes from the root deflection. Under high frequency, the shaft bending increases significantly, and the displacement response is produced by the combination of shaft bending and root deflection. The changes of F-actin content in the cochlea exposed to noise would affect the stereocilia stiffness. In this paper, it is found that the decrease of stereociliary Young's modulus will increase the peak value of normalized tension and decrease its peak frequency, and the amplitude of normalized tension will increase under the low frequency shear load. Since tip-link is connected to ion channels, the change of normalized tension will affect the probability of ion channels opening, change the cochlea's perception ability to the sound of corresponding frequency, and then affect the frequency selectivity of hair bundle. Therefore, previous studies of stereocilia as rigid bodies have led to the underestimation of the response of the cochlea to low-frequency acoustic signals. This model accurately describes the law of tip-link tension and provides a corresponding theoretical explanation for hearing impairment caused by noise environment. Previous experiments have shown that lymphatic viscous resistance has little effect on the deflection of stereocilia. In this paper, when the viscous resistance is ignored, the tip-link tension changes very little, and when the pressure between the stereocilia is ignored, the tip-link tension changes significantly and the resonance peak of f2 disappears. Therefore, lymphatic fluid regulates the resonance properties of the tip-link tension by creating pressure between the stereocilia. The presence of lymphatics is essential for the generation of the frequency characteristics of the hair bundle. In the low frequency domain, stereocilia motion is mainly regulated by tip-link, and in the high frequency domain, it is mainly regulated by lymphatic pressure.