To clarify the mechanism of unfavorable effects of wind on cooling efficiency of dry cooling towers full scale measurements and wind tunnel modeling were conducted. A hot water circulation system and fin-tubular radiators were used for simulating the thermodynamic process of dry cooling towers. A dimensionless parameter, wind effect coefficient Cw, was defined and measured to describe the wind effects on the efficiency of cooling tower radiators. The experimental results suggest that in the regular speed region the natural wind lowers the efficiency of dry cooling towers because of three reasons: (1) formation of an unfavorable pressure distribution at the tower entrance, (2) breaking of the hot plume rising from the cooling tower, (3) cool air induced by leading edge separation enters the cooling tower.