Tailrace tunnel ventilating can be used as a highly efficient and energy saving air conditioning for factory buildings in hydropower station. This paper describes an improved model of heat and moisture transfer for tailrace tunnel ventilating system with the assumption of thermal insulated for the tunnel wall and with the same temperature at any cross section as the wet bulb temperature of that air, and the improved model has been validated against the field test from Yingxiuwan hydropower station and compared with the reference simplified model, the results show that the improved model has a good agreement with the field test data and a better precision than the reference simplified model for the performance prediction of heat and moisture transfer of tailrace tunnel ventilating, especially for the short tunnel system. Moreover, the thermodynamic calculation method of heat and moisture transfer is presented, and the method is intended for use in annual performances prediction or design tools for tailrace tunnel ventilating system in hydropower station. (C) 2009 Elsevier Ltd. All rights reserved.