Objective In order to provide a theoretical basis for the structural design of stents, the mechanical properties of polymeric vascular stents considering size effect were investigated, and the influence law of stent structure on the mechanical properties of stents and size effect during stent deformation was further analyzed. Methods The Cosserat theoretical model of PLA considering size effect was established, and combined with the finite element method, the bending stiffness and radial support strength of the stent were obtained by three-point bending and flat plate compression, and the influence laws of the rib thickness and rib width of the stent, the radius of curvature and axial spacing of the bracing unit on the radial support performance and size effect strength of the bracket were further analyzed. Results there was significant size effect in both bending and compression of the polymeric vascular stent. The radial support strength of the support unit is negatively correlated with the radius of curvature and axial spacing, and positively correlated with the rib thickness and rib width, and the smaller the radius of curvature, axial spacing, rib thickness and rib width of the support unit, the larger the size effect strength in compression. Conclusions the radial support performance of the stent is mainly determined by the stiffness of the structure and is affected by the strength of the size effect in the process of structural deformation. The smaller the characteristic dimensions of the stent structure and the greater the degree of stent’s bending and twisting deformation, the more pronounced the size effect and the greater the increase in the radial support performance of the stent.