A method for controlling the freezing capacity of a fixed-frequency freezing AC ice-water system, by using temperature buffer difference of individual requirement ends to control the number of operating compressors in a fixed-frequency chiller and make each of the operating compressors have a usage rate close to 100%. Further, various operating procedures are defined for the requirement ends and each of the operating procedures has an individually defined high-low temperature range such that the freezing capacity supply cycle or startup cycle of the fixed-frequency chiller can be adjusted by using the high-low temperature ranges of the operating procedures as temperature buffer strips, thereby allowing the compressors in the fixed-frequency chiller to operate collectively in order to save energy.