The　low　and　middle　temperature　Organic　Rankine　Cycle　could　be　used　to　recover　the　low　grade　waste　heat.　The　conditions　of　the　engine　exhaust　gas　vary　in　a　range　when　the　vehicle　is　running.　It　is　difficult　to　confine　the　operation　condition　of　ORC　at　a　fixed　point.　In　this　paper　the　performances　of　different　working　fluids　operating　in　a　certain　region　instead　of　a　single　point　were　analyzed　using　a　thermodynamic　model　built　in　Matlab　together　with　REFPROP.　The　results　of　9　different　pure　organic　working　fluids　were　compared　in　their　regions　when　the　net　power　output　was　the　same　value.　The　safety　levels　and　their　impacts　to　the　environment　were　also　evaluated.　The　results　indicate　that　R11　and　R141b　manifest　the　best　thermodynamic　performances;　however　R236ea　and　R245ca　are　the　most　environment　friend　working　fluids　for　the　engine　waste　heat　recovery　application.