In order to reduce the temperature gradient of the laser irradiation zone of the light guide mirror surface, the three-dimensional steady turbulent flow and heat transfer equations are solved with the finite volume method, and the temperature field of the laser irradiation zone is analyzed. The effects of rectangular channel size, concentration and velocity of coolant on average temperature rise and temperature rise difference of the light guide mirror surface are studied. Accordingly, a dual-channel structure is designed. Results show that for the single channel, the temperature field of the irradiation zone is not symmetrical around the geometric center and the highest temperature point is located at the downstream of the irradiation zone. The heat transfer efficiency can be improved by the increase of the cross-section size and the coolant velocity. In addition, the temperature distributions between the different surfaces of the channels are not the same. The higher the concentration of the ethylene glycol coolant, the worse the heat transfer effect. The average temperature and the temperature rise difference of the dual-channel structure can be reduced by up to 17.79% and 67.97%, respectively, compared with those of the single-channel structure.