In order to investigate dynamic behaviors of a 500W@ 4.5K helium refrigerator,the process simulator has been completed. The cryogenic process model is described and main components are customized. The realtime communication between the process model and the control system has been achieved. Compared with the preliminary experimental data,the errors of temperatures during the process of 300 K-80 K are less than 10%.The process model is validated to predict the cool-down process very well. The controller parameters are tuned in simulation and applied to the actual refrigerator suitably. Based on the dynamic simulation,the operation of Joule-Thomson( JT) by pass valve has been optimized. And the cool- down process from 300 K to 4. 5 K has been simulated under the control programs. Simulation results indicate that this dynamic simulator based on actual control architecture is available to process control and operation optimization for the helium refrigerators. The order of investigate of behaviors of a 500W @ 4.5K helium refrigerator, the process simulator has been completed. The cryogenic process model is described and main components are customized. The realtime communication between the process model and the control system has been achieved with the preliminary experimental data, the errors of temperatures during the process of 300 K-80 K are less than 10%. The process model is validated to predict the cool-down process very well. The controller parameters are tuned in simulation and applied to Based on the dynamic simulation, the operation of Joule-Thomson (JT) by pass valve has been optimized. And the cool-down process from 300 K to 4.5 K has been simulated under the control programs. Simulation results indicate that this dynamic simulator based on actual control architecture is available to process control and operation optimization for the helium refrigerators.