A　dual　loop　organic　Rankine　cycle　(DORC)　system　is　designed　to　recover　waste　heat　from　a　heavy-duty　compressed　natural　gas　engine　(CNGE),　and　the　performance　of　the　DORC　CNGE　combined　system　is　simulated　and　discussed.　The　DORC　system　includes　high-temperature　(HT)　and　low-temperature　(LT)　cycles.　The　HT　cycle　recovers　energy　from　the　exhaust　gas　emitted　by　the　engine,　whereas　the　LT　cycle　recovers　energy　from　intake　air,　engine　coolant,　and　the　HT　cycle　working　fluid　in　the　preheater.　The　mathematical　model　of　the　system　is　established　based　on　the　first　and　second　laws　of　thermodynamics.　The　characteristics　of　waste　heat　energy　from　the　CNGE　are　calculated　according　to　engine　test　data　under　various　operating　conditions.　Moreover,　the　performance　of　the　DORC　CNGE　combined　system　is　simulated　and　analyzed　using　R245fa　as　the　working　fluid.　Results　show　that　the　maximum　net　power　output　and　the　maximum　thermal　efficiency　of　the　DORC　system　are　29.37　kW　and　10.81%,　respectively,　under　the　rated　power　output　condition　of　the　engine.　Compared　with　the　original　CNG　engine,　the　maximum　power　output　increase　ratio　and　the　maximum　brake　specific　fuel　consumption　improvement　ratio　are　33.73%　and　25%,　respectively,　in　the　DORC-CNGE　combined　system.