This　paper　presents　the　relation　between　the　parameters　of　working　fluids　and　output　net　power　for　supercritical　cycle　of　medium-temperature　geothermal　power　generation,　and　confirms　the　optimal　operation　parameters　and　the　selection　standard　of　working　fluids.　The　influence　of　temperature　of　geothermal　fluid　and　the　inlet　parameters　of　expander　on　the　output　net　power　of　the　cycle　were　simulated　by　the　EES　software.　The　results　show　that　the　inlet　temperature　of　expander　is　higher　when　the　output　net　power　reaches　the　maximum,　so　the　hydrocarbons　and　other　new　working　fluid　should　be　selected　as　working　fluids.　The　output　net　power　can　reach　an　optimum　by　choosing　an　appropriate　inlet　temperature　of　the　expander　when　the　temperature　of　the　geothermal　fluid　and　the　inlet　pressure　of　the　expander　were　constants.