In the counter-current tower, the air distribution device comprises an air inlet and an air guide device; In the cross-flow tower, it only refers to the air inlet, and its form, size and air inlet mode must be determined. The air inlet of the counter-current tower refers to the space from the bottom of the packing to the top of the water surface of the collecting basin. If the air inlet area is large and the air inlet speed is low, it will not only make the air in the tower evenly distributed and reduce the airflow resistance, but also increase the height of the tower and increase the cost. On the other hand, if the air inlet area is small, the wind speed distribution is uneven, and the vortex area of the air inlet is large, it will affect the cooling effect. The ratio of the air inlet area to the water spraying area of the ventilation counter-current tower should not be less than 0.5. When it is less than 0.5, a wind guide device should be set to reduce the air inlet vortex. In addition, Article 6.3.2 of Technical Design Code for Mechanical Ventilation Cooling Towers stipulates that the height of air inlet shall be determined according to the ratio of air inlet area to packing area. The ratio of air inlet area to packing area is selected according to the following conditions: unilateral air inlet should be 0.35 ~ 0.45; The air inlets on both sides should be 0.4 ~ 0.5; Three-side air intake should be 0.45 ~ 0.55; The air intake in all directions should be 0.5 ~ 0.6.