The temperature distribution of the accurate biological tissues in different powers and different irradiation times is the premise of efficacy of laser-induced interstitial thermotherapy assessment. A three-dimensional finite element heat transfer model was constructed by multi-physical field conductive coupling analysis software COMSOL Multiphysics in the invariable tissue optics parameters situation. The model was based on Pennes bio-heat transfer equation and axisymmetric Gaussian shape of the laser beam heat equation. In this model, the parameters were for the liver tissue in vitro, and the thermal properties of biological tissue density, specific heat and thermal conductivity with temperature variations were considered. The temperature field data sets were obtained by simulation under the laser power for 0.77 W, 0.95 W, 123 W, irradiation time for 10~90 s, radial distance range 0~2 mm and axial distance range 0~4 mm. Fitting algorithm was used to obtain the tissue′s temperature distribution model related to the laser power, irradiation time, radial and axial distance. The results of 0.88 W and 1.05 W were compared with the Pennes equation, and the error between them was within 5%.