Based on the histological characteristics, a three-dimensional model of the vein and its surrounding tissues was constructed. The light distribution of the irradiated vein was simulated by diffusion approximation theory, the biological thermal equation was solved by finite element method to obtain the temperature distribution throughout the tissue, and the damage caused by laser irradiation was calculated according to the Arrhenius equation. The photothermal response of a radial fiber and a radial 2ring fiber was compared. The effects of laser power, pull-back speed, linear endovenous energy density and venous diameter on the therapeutic effect of the radial 2ring optical fiber were discussed. The results show that the temperature of the tissue irradiated by the radial 2ring fiber is lower than that by the radial fiber, and the adhesion between the fiber and vascular wall could be reduced. When the tissue is irradiated by the same linear endovenous energy density, it is more secure in the lower laser power treatment. The larger the vein diameter, the higher the linear endovenous energy density is required to achieve the therapeutic effect. The proposed model is helpful to better understand the action mechanism of the endovenous laser ablation.