The invention relates to an optimization method for a peak cooling system of an air cooling unit, and belongs to the technical field of air cooling unit design of power stations. According to the known conditions of an air-cooling island characteristic curve, a turbine micro-increase power curve, environmental meteorological parameters, the surplus amount of water resource, the cost of electricityof a power plant, equipment price parameters of the air cooling unit and the like, and by calculating economic data such as equipment investment and operating cost, important equipment parameters such as optimized peak condenser area, circulating water volume, and mechanical tower configuration are determined. The optimization method for the peak cooling system of the air cooling unit is more consistent with application, the important equipment parameters such as the optimized peak condenser area, the circulating water volume, and the mechanical tower configuration are finally determined, theequipment configuration is more reasonable, and the unit operation economy is good.