The thermal buoyancy effect was introduced into model tests on a direct air-cooled condenser (ACC) for a large power plant in wind tunnel simulation. In order to get thermal flow field of air-cooled tower, PIV experiments are performed and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of direct air-cooled system also.