Abstract: In order to recover the pressure energy of the pipeline below 6 MPa in the natural gas letdown station, the high pressure single screw expander (HPSSE) with a diameter of 117 mm was independently developed in laboratory. The high pressure air was used as the working medium, and the performance of this HPSSE was tested by changing the inlet, outlet pressure and rotational speed. The variation rules of performance parameters were obtained. Results show that the maximum inlet pressure, output power, volumetric efficiency, shaft efficiency, and lowest air-consumption ratio is 5.8 MPa, 56.5 kW, 91.8%, 51.9%, and 66.4 kg/(kW·h), respectively. The volumetric efficiency increased with the increase in the rotational speed, the volumetric efficiency was immensely affected by inlet pressure under fairly slow rotational speed and a slight change in volumetric efficiency was observed under considerably high rotational speed. The shaft efficiency increased with the increase in the rotational speed, and the shaft efficiency initially increased and gradually stabilized thereafter with the increase in the inlet pressure. The HPSSE adopted the axial discharge technology, which relieved the under expansion and extended the high efficient operation area. The experimental results provide technical support for demonstration project of the pressure energy recovery by using HPSSE in the next stage.