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.　©　2018,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.