Abstract: In the simulated water environment, the stiffness test of the shrinkage specimen of Hold Down Spring of The Reactor Internals was carried out, and compared with the analysis results of the finite element simulation, theoretical model based on small disturbance and the large disturbance follow-up model. The results show that when the friction coefficient is 0.189 according to the experimental value of the literature, the finite element simulation, the stiffness value calculated based on the small disturbance theory model and the large disturbance follow-up model are similar to those obtained by the test; The stiffness of the unloading stable section is significantly smaller than that of the loading stable section, which is about 0.6 times that of the loading. The finite element simulation analysis further clarifies that during the deformation process of Hold Down Spring, the section of Hold Down Spring has a rotation, and the contact point between it and the pad is not fixed, and there is a radial displacement back and forth in the process of loading and unloading. Moreover, the direction of the frictional force on the contact surface of the Hold Down Spring is reversed, so that there is a large difference in the stiffness of the Hold Down Spring during the loading and unloading process. To compare with theoretical model based on small disturbance, the results obtained by considering the large disturbance follow-up model of the Hold Down Spring section rotation and the radial displacement of the contact point are closer to the finite element simulation.