Abstract: In order to achieve a high cooling efficiency of a high power Yb:YAG laser, its water cooling structural was designed, and the heat transfer effect of this structure was simulated by means of finite element method. Surface coefficient of heat transfer and the temperature distribution on the heat exchange surface were obtained. The results indicate that the distribution of the transfer coefficient and the temperature is uniform distribution in this structure. The coefficient of heat transfer reached 1.8104W/(m2K) and the temperature difference on the surface was less than 1K, which indicate a good heat transfer effect.