Abstract: Pumping well water to melt ice is one of the most effective measures to resolve the ice problem for diversion power station in high altitude and cold regions. In order to investigate the water temperature attenuation process of diversion channel for pumping well water to melt ice in winter, the prototype observations were conducted at Hongshanzui Hydropower Station in February 2013 and January 2014, respectively, which verified the numerical simulation results. Based on the numerical simulation results in the RNG k-ε model, the water temperature attenuation process of diversion channel was analyzed from the point of heat flux ratio. The analysis reveals that the water temperature attenuation process included three periods:rapidly-reducing period, transitional period and slowly-descending period. Each period was influenced by different thermal conditions. In addition, the curve of water temperature attenuation followed a power function with a correlation coefficient of 0.98. Compared the water temperature attenuation processes with the changes of atmospheric temperature, the attenuation rate of water temperature significantly increased with the decrease of atmospheric temperature. The turning point of the water temperature attenuation process was at -10℃. When the atmospheric temperature was above -10℃, the attenuation law of water temperature remained consistent and was mainly influenced by the ratio of heat flux. However, if the atmospheric temperature was below -10℃, it significantly affected the channel water temperature.