Large scale helium liquefaction/refrigeration plant plays a vital role in advanced large equipment such as fusion reactors and accelerators. A new helium liquefaction cycle with double stage compressor is proposed in this paper, which is different from the Collins cycle. The helium gas from the compressor is divided into two parts. The medium-pressure helium gas as one part flows through the heat exchangers and is liquefied by throttling in the valve. The other part, high-pressure helium gas flows into the turbine for adiabatic expansion with decrease of its temperature and pressure. Both high-temperature helium gas streams become low-temperature and low-pressure. In this paper, the new cycle is parametrically analysed to demonstrate the effect of each parameter on the performance of the cycle. The results of the liquefaction capacity are obtained in different working conditions. Exergy analysis, which is an effective way to analyse thermodynamic cycles, is performed on the liquefaction process and the result is significant for the appropriate design of helium liquefaction system.