The　characteristics　of　a　vehicle　diesel　engine　exhaust　gas　under　various　operating　conditions　were　studied　experimentally　and　a　set　of　organic　Rankine　cycle　(ORC)　was　designed.　The　effects　of　four　kinds　of　pure　fluids,　four　kinds　of　azeotropic　mixtures　and　four　kinds　of　zeotropic　mixtures　on　the　performance　of　ORC-engine　combined　system　under　various　operating　conditions　were　compared　and　analyzed　by　simulation.　Results　show　that,　with　the　increase　of　engine　speed　and　accelerator　opening,　the　net　power　outputs　of　the　ORC　system　for　these　twelve　organic　working　fluids　and　the　exergy　destruction　rates　of　system　and　its　components　as　well　gradually　increase,　but　the　growth　rates　are　different.　The　averaged　net　power　output　of　the　ORC　system　for　R504　under　various　operating　conditions　of　diesel　engine　gives　its　maximum　value　of　7.29　kW,　which　is　18%　higher　than　R227ea.　The　ORC　system　thermal　efficiency　of　mixed-refrigerants　is　generally　higher　than　that　of　pure　working　fluids.　The　exergy　efficiency　of　ORC　system　for　zeotropic　mixture　increases　by　14%　than　that　of　pure　mixtures　and　R415B　gives　the　maximum　value.