Abstract: In order to solve the problem of insufficient output of mechanical draft dry cooling tower which can’t meet the cooling demand in summer, a mechanical draft dry cooling tower with wet medium pre-cooling inlet air system is designed in this paper. The influence of wet medium thickness, ambient temperature and humidity on the operating performance of the designed dry cooling tower and water-saving performance are carried out by using Matlab program. The results show that 300 mm CELdek7060 medium pre-cooling inlet air system has the best pre-cooling effect and the heat rejection rate of the cooling tower increases by 20.57% at the ambient temperature of 26 ℃ and humidity of 57%; the heat rejection performance of the dry cooling tower decreases with the increases of ambient temperature, and there is a critical temperature of 13.5 ℃; the wet medium pre-cooling system could improve the heat rejection rate of dry cooling tower by 96.96%, and further reduce the outlet water temperature by 2.80 ℃ at the ambient temperature of 35 ℃ and humidity of 57%; the wet medium pre-cooling system could improve the heat rejection rate of dry cooling tower by 81.14%, and reduce the outlet water temperature by 6.81 ℃ at the ambient temperature of 26 ℃ and humidity of 0%. The total annual energy-saving benefit of a single tower is about 138 400 yuan, which has good economic benefits.