To　efficiently　recover　the　waste　heat　from　a　diesel　engine　exhaust,　a　regenerative　organic　Rankine　cycle　(RORC)　system　was　employed,　and　butane,　R124,　R416A,　and　R134a　were　used　as　the　working　fluids.　The　resulting　diesel　engine-RORC　combined　system　was　defined　and　the　relevant　evaluation　indexes　were　proposed.　First,　the　variation　tendency　of　the　exhaust　energy　rate　under　various　diesel　engine　operating　conditions　was　analyzed　using　experimental　data.　The　thermodynamic　model　of　the　RORC　system　was　established　based　on　the　first　and　second　laws　of　thermodynamics,　and　the　net　power　output　and　exergy　destruction　rate　of　the　RORC　system　were　selected　as　the　objective　functions.　A　particle　swarm　optimization　(PSO)　algorithm　was　used　to　optimize　the　operating　parameters　of　the　RORC　system,　including　evaporating　pressure,　intermediate　pressure,　and　degree　of　superheat.　The　operating　performances　of　the　RORC　system　and　diesel　engine-RORC　combined　system　were　studied　for　the　four　selected　working　fluids　under　various　operating　conditions　of　the　diesel　engine.　The　results　show　that　the　operating　performances　of　the　RORC　system　and　the　combined　system　using　butane　are　optimal　on　the　basis　of　optimizing　the　operating　parameters;　when　the　engine　speed　is　2200　r/min　and　engine　torque　is　1215　Nm,　the　net　power　output　of　the　RORC　system　using　butane　is　36.57　kW,　and　the　power　output　increasing　ratio　(POIR)　of　the　combined　system　using　butane　is　11.56%.