An experimental test system including the oil circulation system and the gas circuit system has been designed and built to explore the effects of the lubricating oil flow rate on the performance of a single-screw compressor, used in a portable natural gas liquefaction process. Outlet pressure, outlet volumetric flow rate, volumetric efficiency, and specific power rate are the parameters for evaluation of the energy performance of the single-screw compressor. The experimental results indicate that the outlet pressure and outlet volumetric flow rate can be effectively increased by increasing the flow rate of the lubricating oil at different rotational frequencies and that a certain amount of lubricant oil is helpful to improve the volumetric efficiency. In terms of the specific power rate, the optimum oil-gas ratios are 0.7%, 0.93%, and 1.79%, and the corresponding outlet pressures are 0.45, 0.45, and 0.48 MPa at the conditions of 50, 40, and 30 Hz, respectively.