Laser-induced damage threshold (LIDT) is investigated at several wavelengths in the high-purity silica optical fiber. The finite element method (FEM) is used to study transmission mode, LIDT, temperature distribution, and thermal stress distribution of the fiber. Our results show that the center of the front surface is subjected to severe thermal effects under laser irradiation and consequently, and it is susceptible damage. The variations in temperature and thermal stress are identified as increasing with laser fluences, which show a similar tendency. When laser fluences surpass the LIDT, such as 35 GW / cm², the temperature at the front surface center shows a sudden growth and the melting damage appears, and no stress damage occurs at this time. Notably, the melting effect of high purity fused silica optical fiber is simulated by numerical calculation based on ray optics for the first time. Our research can provide systematic FEM simulations for the LIDT of silica optical fibers.