To　reuse　the　diesel　engine　of　waste　heat　in　exhaust,　organic　Rankine　cycle　(ORC)　was　proposed.　R245fa　(1,　1,　1,　3,　3-pentaflu-oropropane)　was　used　as　the　working　fluid　in　the　ORC　system.　Final　exhaust　temperature,　net　work　and　actual　efficiency　of　ORC　were　studied　under　different　evaporating　temperature　and　cooling　temperatures.　The　results　show　that　primary　expansion　system　should　be　selected　when　the　evaporating　temperature　is　lower　than　367.46　K.　However,　when　the　evaporating　temperature　is　higher　than　367.46　K　but　lower　than　404.6　K,　two-level　expansion　system　is　recommended.　For　a　fixed　cooling　temperature,　final　exhaust　temperature　is　decreased,　but　net　work　and　actual　efficiency　of　ORC　are　increased　with　the　increase　of　the　evaporating　temperature.　Under　a　given　evaporating　temperature,　final　exhaust　temperature　is　decreased,　but　net　work　and　actual　efficiency　of　ORC　are　increased　with　the　decrease　of　cooling　temperature.