Abstract: In view of problems of large installed capacity, high power consumption and characteristics of stage in freezing construction method, a frequency-conversion energy-saving system based on PLC was designed based on analyzing mechanical properties of screw brine units of freezing system under different working conditions and power consumption in various frozen phases. The system takes PLC as control core, makes information feedback of system condition by use of pressure sensor and liquid level gauge , and uses PID algorithm to control frequency output of frequency converter so as to regulate flow of salt water pump and control amount of cooling. The feasibility and high efficiency of application of the system in shaft construction was proved by experimental data.