The　thermodynamic　performance　limits　of　power　cycles　are　governed　not　only　by　the　first　and　second　law　of　thermodynamics,　but　also　by　the　cycle　configuration　and　working　fluid　properties.　The　organic　Rankine　cycle　(ORC)　is　a　promising　technology　for　low-and-medium　temperature　heat　utilization.　This　work　further　develops　the　thermodynamic　performance　limits　analysis　framework　of　sub-and　trans-critical　ORCs　under　realistic　heat　source　conditions,　and　investigates　the　impact　mechanism　of　key　property　parameters　on　system　performance.　Working　fluid　thermodynamic　properties　are　characterized　using　a　corresponding　state　model　with　5　property　parameters　that　are　usually　available　in　the　early　stages　of　system　design.　The　property　and　system　parameters　are　optimized　simultaneously　using　a　multi-objective　genetic　algorithm.　The　thermodynamic　performance　limits,　and　the　optimal　working　fluid　properties　and　system　operation　conditions　are　identified.　The　obtained　limits　represent　the　highest　performance　of　ORC.　The　obtained　optimal　property　and　system　parameters　represent　the　desired　working　fluid　and　system　operation　characteristics.　The　impact　mechanism　of　key　property　parameters　on　system　performance　is　discussed　in　detail　in　a　sensitivity　analysis.　It　is　found　that　the　critical　tem-perature　is　the　most　important　property　parameter,　and　that　it　changes　the　preference　over　efficiency　and　compactness　objectives.　The　obtained　thermodynamic　performance　limits,　optimal　parameter　sets,　and　impact　mechanism　provide　insights　for　working　fluid　selection　in　ORC　research　and　implementation.　(c)　2021　Elsevier　Ltd.　All　rights　reserved.