With the influence of the different gas Reynolds number and liquid Reynolds number on falling film heat and mass transfer of subway station plate evaporative cooler, the experiment was carried out by noncontact infrared thermal imaging technology under gasliquid crossflow condition. The results indicated that during the increasing of liquid Reynolds number the thickness of liquid film increased and the temperature difference between liquid film inlet and outlet decreased in determined heating water temperature which weakened the heat transfer of liquid film. However, the increase of liquid Reynolds number strengthened the liquid film turbulence that enhanced heat transfer. Under the synergistic effect of these two factors, there was an optimal liquid Reynolds number which minimize thermal resistance and maximize heat and mass transfer coefficient of liquid film.