Energy　saving　and　environment　protection　are　two　most　important　issues　that　today＇s　internal　combustion　engine　industry　must　tackle　with.　Lots　of　heat　energy　waste　with　the　exhaust　gas　when　the　engine　is　running.　Organic　Rankine　cycle　(ORC)　is　a　good　method　to　recover　the　waste　heat　of　the　engine　exhaust.　In　this　paper,　the　mathematical　model　of　ORC　was　built　up　in　Matlab　and　the　parameters　were　optimized　using　genetic　algorithm　(GA).　Eight　pure　component　organic　working　fluids　were　selected　and　compared.　The　results　indicate　that　the　evaporating　pressure　of　the　working　fluid　and　the　condensing　temperature　are　two　important　parameters　for　ORC;　the　super　heater　also　can　enhance　the　system　thermal　efficiency　slightly.