The invention provides an anti-freezing system and method for a direct air-cooling unit. The anti-freezing system comprises a turbine, an electric generator and an air cooling island system. The turbine and the electric generator are connected through a coupler. A steam exhaust opening of the turbine is connected with the air cooling island system. The air cooling island system comprises six rows of air cooling condenser systems of the same structure. By means of the pressure measuring point and the temperature measuring point, automatic control over an air-cooling fan by the super-cooling degree of condensed water is achieved, thus, back pressure of the unit is effectively controlled, after a PID controller is utilized for controlling the rotating speed of the fan, the requirement of the back pressure of the unit and the anti-freezing protection requirement of an air-cooling island can be met, meanwhile, the power consumption rate of the fan can be reduced, the power utilization rate of a power plant is reduced, and the purposes of energy saving and efficiency improving are achieved on the premise of ensuring that the unit is safe and reliable.