In order to reduce the thermal deformation of the light guide mirror, the finite volume method was employed to solve the three-dimensional turbulent heat transfer equation and the temperature field of the laser irradiated region was obtained. In this thesis, the effects of laser power, irradiation time, coolant velocity, mirror materials, the distance between channel and mirror on the temperature field were discussed. The average temperature and the standard deviation of temperature of irradiation zone were regarded as the main indexes to evaluate the cooling effect. It is found that the greater the laser power is, the greater the temperature in various directions is. The temperature rise is faster in the initial stage of laser irradiation and it tends to be gradual in the latter. The larger the coolant velocity is, the lower the average temperature and the standard deviation of temperature are. Different properties of the mirror materials also have influence on the heat transfer effect, but the distance between channel and mirror has little effect on the temperature field of the copper mirror.