A double-pressure helium liquefaction cycle, which consists of two compressors, six heat exchangers, two expanders and several valves, was proposed in this paper. The thermodynamic parameters of the process were calculated and analyzed. The mathematical models of the above-mentioned key equipment are established, and the cool down process of the helium refrigerator is dynamically simulated. By adjusting the parameters of each valve in the process, the working process of the compressor was simulated, and the cool-down process of heat exchangers and the expanders was obtained and analyzed. Finally the stable refrigeration capacity was obtained. The simulation of the dynamic process has a great guiding role for the actual experimental process afterwards.