Propagation of 808nm wavelength laser beam in liver tumors was simulated with Monte Carlo method. Based on the distribution of light in normal liver and liver tumors, the temperature distribution inside tissue under laser irradiation has been retrieved. Furthermore, the influences of laser power and action time on the temperature field were studied. The results show that the normal liver and liver tumors have different light absorption with laser beam. The difference of temperature distribution in tissues with the same laser power is useful to be applied in control the treatment of laser-induced interstitial thermotherapy for liver tumors.