Abstract: A nitrogen cryogenic refrigeration cycle system of the High Energy Photon Source (HPES) has been designed for cooling of 7 superconducting RF cavity cryostats in the storage ring. The purpose of thermodynamic analysis of the nitrogen cryogenic refrigeration cycle system combined the cryostat’s characteristics and studied the cycle progress. A thermodynamic analysis model of the system was built, and the relationship between refrigeration coefficient and pressure ratio of the system was also carried out. According to the overall layout of the system, the available energy loss of nitrogen compressor and cryogenic turbine expander were analyzed. And optimization thermodynamic parameters of the system were also achieved. For the nitrogen cryogenic refrigeration cycle system, the results will be a guiding significance in optimal design and engineering practice in the future.