[en] When outdoor air flowing through the tailrace tunnel, it will be handled and its thermodynamic conditions will change under the differences of temperature and water vapor pressure between air and water surface, air and tunnel wall. Utilizing the handled air for space cooling in hydropower station is an energy saving, environmental protection and renewable application of natural cold source. In this paper, a detailed quasi-three-dimensional mathematical model of heat and mass transfer of tailrace tunnel ventilation is established based on the analysis of heat and moisture transfer during the air flowing through the tunnel. And the model has been validated against the field test data from Yingxiuwan hydropower station. Besides, the model is used for performance simulation of tunnel ventilation for a real great hydropower station, and the conclusions show that the air condition is gradually close to the saturation corresponding the water temperature with ignored the effect of long-term thermal cumulative of the tunnel rock, and the heat and moisture transfer between air and water surface is dominant, which has a ratio of 80%–90% in the total heat and moisture exchange. - Highlights: • We developed a mathematical model of heat and mass transfer of tailrace tunnel ventilation. • The field tests were conducted to validate the heat and mass transfer model. • The outlet air parameters of tunnel are close to the saturation corresponding the water temperature. • It is feasible to provide a free cooling for hydropower station by utilizing tunnel ventilation.