The fermentation process is an extremely important part of the fuel ethanol production process, and the temperature of the mature mash during the fermentation process directly affects the yield and efficiency of fuel ethanol fermentation. In order to solve this problem, this paper adopts Honeywell's PKS system to design a control system for the outlet temperature of the heat exchanger in the liquefaction plant. The Profit Loop algorithm is used to replace the conventional PID control method. The results show that the improved system has higher control accuracy and can be popularized in the field of engineering applications.