A　single-screw　expander　with　195　mm　diameter　is　developed　to　recover　pressure　energy　in　letdown　stations.　An　experiment　system　is　established　using　compressed　air　as　a　working　fluid　instead　of　natural　gas.　Experiments　are　conducted　via　measurements　for　important　parameters,　such　as　inlet　and　outlet　temperature　and　pressure,　volume　flow　rate　and　power　output.　The　influence　of　inlet　pressure　and　rotational　speed　on　the　performance　are　also　analyzed.　Results　indicate　that　the　single-screw　expander　achieved　good　output　characteristics,　in　which　2800　rpm　is　considered　the　best　working　speed.　The　maximum　volumetric　efficiency,　isentropic　efficiency,　overall　efficiency,　and　the　lowest　air-consumption　are　51.1　kW,　83.5%,　66.4%,　62.2%,　and　44.1　kg/(kW.h),　respectively.　If　a　single-screw　expander　is　adopted　in　a　pressure　energy　recovery　system　applied　in　a　certain　domestic　natural　gas　letdown　station,　the　isentropic　efficiency　of　the　single-screw　expander　and　overall　efficiency　of　the　system　are　found　to　be　66.4%　and　62.2%,　respectively.　Then　the　system　performances　are　predicted,　in　which　the　lowest　methane　consumption　is　27.3　kg/(kW.h).　The　installed　capacity　is　estimated　as　204.7　kW,　and　the　annual　power　generation　is　43.3　MWh.　In　the　next　stage,　a　pressure　energy　recovery　demonstration　project　that　recycles　natural　gas　will　be　established　within　China,　with　the　single-screw　expander　serving　as　the　power　machine.