High condensing pressure of air cooling condenser (ACC) at high environmental temperature in summer is a common problem of air-cooling power generating units. The wavy finned flat tube bundle is the key element of ACC. Experiments on heat transfer enhancement of wavy finned flat tube bundle by water spray cooling was carried out by wind tunnel with a visualized window for temperature distribution measurement of fin surface. The mechanisms of heat transfer enhancement, including that of the cooling of air due to upstream droplets evaporation and the evaporation of water film formed by droplets impacting on the finned tubes, were investigated, respectively. The cooling efficiencies for different inlet air velocities were required. While the air flow Reynolds number ranges from 210 to 680, the experimental correlations of flow and heat transfer were obtained. As compared to the case without spray, the Nusselt numbers of three water flow rates are increased by 48%, 56% and 68% on average, respectively. The respective contributions of both pre-cooling and water film evaporation were evaluated, which were almost equal as the Reynolds number is about 500. The results can benefit the optimization of spray cooling technique used in air cooling condenser. (C) 2017 Elsevier Ltd. All rights reserved.