Abstract: In clinical treatment, stenosed vertebral arteries with different diameter require different dilatation size of stents. The dilatation size of a stent has a great influence on its mechanical properties. The finite element method was used to simulate and analyse the expansion process in vitro of three different stents to investigate the effect of different dilatation size on stents' mechanical properties with the same structure. Results showed: 1) with the increase in the final expansion diameter of stents, the maximum equivalent stress, axial shortening rate, expansion non-uniformity and flexibility of the three stents had an increasing tendency, while radical bracing stiffness and static safe-value decreased; 2) the radial spring-back of stents was mainly influenced by the material and structure, the dilatation size didn't play the decisive role; 3) comparisons showed that the theoretical and experimental data matched well, and the error values were under 7% which proved the veracity and rationality of the finite element simulation; 4) the treatment effect of stents was verified with animal experiment, and the result showed the implantation of stents was safe and effective. This study proved the dilatation size has a great influence on the treatment effect of stents. In the meantime, it is expected to offer a theoretical basis for the smooth implementation of clinical treatment.