Abstract: In this study, the variable capacity refrigeration system based on PID control was proposed, aiming to simultaneously realize the functions including quick-freezing, refrigeration and precooling. Simulation of the flow field in the storage was performed by ANSYS Fluent to predict the distribution of flow field. PID logic was used to regulate the hot gas bypass opening valve, and control the mixing ratio of high and low temperature refrigerants, so that the cold storage could quickly respond to dynamic load changes, the evaporation temperature could become stable faster with small fluctuation and high control accuracy. Results showed that the error between simulation model and measured wind speed was within 9%, and the model could reflect the flow field inside refrigerator.When the air supply outlet opening rate was 0.9, the flow rate in cold storage presented superior uniformity. It only took 10 min for the refrigeration system to enter freezing mode from quick-freezing mode, the temperature fluctuation in refrigerated mode was less than ±0.2 ℃. The compressor power consumption could be saved about 9.7% compared with the traditional two-position control.