Abstract: The higher operating vacuum pressure of air cooled power plant greatly affects the safety and power output of steam turbine in summer, so the method of reducing air temperature by spray humidification is used. The cooling capacity of air cooled condenser can also be improved by this method. The theoretical process of spray humidification is analyzed in this paper. The method of calculating the adiabatic saturated temperature by programming is given in this paper and the research shows that the adiabatic saturated temperature is the lowest temperature that makes the air saturated by spraying water. The differences between the theoretical humidification and the actual spray processes are compared. The poor supply capacity of water and nozzle spraying are the direct and indirect reasons why the spraying humidification process can not reach the expected effect.