A　calculator　program　with　EES　software　was　designed　for　the　low-medium　temperature　geothermal　power　generation　system　with　organic　Rankine　cycle.　The　optimal　evaporation　temperature　was　obtained　by　theoretical　calculation　for　the　thermal　parameters　and　its　performance　of　the　main　state　points.　The　effects　of　geothermal　fluid　dryness,　its　temperature,　condensing　temperature　and　working　fluid　on　the　optimal　evaporation　temperature　and　net　power　output,　respectively,　were　analysed.　The　results　show　that　for　the　same　working　fluid,　both　optimal　evaporation　temperature　and　net　power　output　increased　with　increasing　geothermal　fluid　dryness　and　its　temperature,　the　optimal　evaporation　temperature　increased　with　increasing　condensing　temperature,　but　the　net　power　output　decreased　with　it.　For　the　different　working　fluids,　when　the　geothermal　fluid　temperature　was　between　80-120°C,　the　optimal　evaporation　temperature　and　net　power　output　of　R601　and　R134a　were　nearly　the　same.　When　the　geothermal　fluid　temperature　was　higher　than　120°C,　no　optimal　evaporation　temperature　of　R134a　existed.　The　net　power　output　of　R134a　was　higher　than　that　of　R601.　©　All　Rights　Reserved.