A research project was undertaken on 1:20 reduced-scale model to investigate the air distribution effectiveness in two supply air modes in the generatrix floor in HOHHOT pumped-storage underground hydropower station. A series of tests (including temperature and air velocity) for 6 cases were performed in 48 various operating conditions. The air distribution was evaluated on the basis of non-uniform coefficient and energy efficiency coefficient principle by calculating dimensionless temperature and the dimensionless velocity. The results showed that mechanical air supply was superior to vertical pressure-gradient air supply. In the mode of mechanical air supply, the best supply air rate and case were determined. Moreover, changing heat sources (50%Q, 75%Q, 100%Q and 125%Q) had little effect on the air distribution in the best supply air case, which verified ventilation effectiveness and reliability. The experimental findings were useful for optimizing the ventilation design in a large space with complex heat sources. (C) 2010 Elsevier B.V. All rights reserved.