According　to　the　analysis　of　heat　balance,　about　1/3　of　the　fuel　combustion　heat　is　taken　away　into　the　ambience　by　exhaust　gas　of　diesel　engine.　Depending　on　the　characteristics　of　the　diesel,　this　paper　uses　a　special　system　to　recover　this　waste　heat,　in　which　the　organic　Rankine　cycle　is　combined　with　a　single　screw　expander.　The　economy　should　be　improved　by　using　this　system　in　the　diesel.　The　model　of　this　system　is　designed　in　Mat　lab　combined　with　REFPROP.　Using　this　way,　the　thermodynamic　parameters　should　be　calculated　and　the　thermodynamic　properties　of　this　system　with　different　working　fluids　should　be　analyzed.　At　last,　R245fa,　R245ca,　R123　and　R141b　are　selected　as　the　alternative　refrigerants　used　in　this　system.