In order to get thermal flow field of direct air-cooled system, the hot water was supplied to the direct air-cooled condenser. The PIV experiments were carried out to get thermal flow field of a direct air-cooled system under different conditions in low velocity wind tunnel, at the same time, the recirculation ratio at cooling tower was measured, so the relationship between flow field characteristic and recirculation ratio of cooling tower can be discussed, from the results we can see that: the flow field configuration fore-and-aft cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed fore-and-aft cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle, the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration fore-and-aft cooling tower reasonably can decrease recirculation ratio under cooling tower, and heat dispel effect of ACC can also be improved.