To study the effect mechanism of air deflectors on dry cooling tower, a three dimensional numerical model was established, with full consideration of the delta structure. The accuracy and credibility of dry cooling tower numerical model were validated. By numerical model, the average air static pressure and the average radial inflow air velocity were computed and analyzed at delta air entry, sector air entry and exit faces. By the air inflow deviation angle theta(d), the effect of air deflectors on the aerodynamic field around tower was analyzed. The water exit temperatures of theta(-1) columns, theta(+2) columns and cooling sectors were also presented to clarify the effect of air deflectors. It was found that the air deflectors improved the aerodynamic field around cooling columns. The reduced air inflow deviation degree at delta entry improved the cooling performance of deteriorated columns. Referring to the radial inflow air velocity u(ra) and the air inflow deviation degree at delta entry, the effect mechanism of air deflectors are clarified under crosswind. (C) 2015 Elsevier Ltd. All rights reserved.