Recovering　the　waste　heat　of　the　flue　gas　from　the　boilers　of　coal-fired　units,　so　that　part　of　the　boiler＇s　flue　gas　waste　heat　can　be　utilized　in　the　turbine　regenerative　heating　system　is　an　important　way　to　increase　efficiency　and　reduce　emissions　of　coal-fired　units.　In　this　paper,　a　600MW　supercritical　coal-fired　unit　is　taken　as　an　example,　and　the　conceptual　design　of　a　flue　gas　waste　heat　cascade　utilization　system　is　carried　out.　Based　on　the　first　and　second　laws　of　thermodynamics,　the　thermodynamic　perfection　of　the　heat　transfer　process　of　the　rotary　regenerative　air　preheater,　the　exergy　efficiency　of　the　heat　displacement　process　of　the　flue　gas　waste　heat　cascade　utilization　system,　and　the　overall　performance　parameters　of　the　coal-fired　unit　are　calculated　and　analyzed　under　different　parameters　such　as　the　bypass　flue　ratio　and　the　inlet　air　temperature　of　the　regenerative　air　preheater.　The　energy-saving　effect　of　flue　gas　waste　heat　cascade　utilization　system　is　restricted　by　factors　such　as　acid　dew　point　temperature,　ammonium　bisulfate　(ABS)　deposition　inside　the　air　preheater,　etc.　Based　on　the　performance　analysis　of　regenerative　air　preheater　and　ABS　deposition　law,　considering　the　structural　characteristics　and　operating　parameters　of　air　preheater,　this　paper　gives　a　criterion　number　(R-number)　of　ABS　deposition　tendency,　and　analyzes　the　actual　operation　performance　of　flue　gas　waste　heat　cascade　utilization　system　considering　the　restrictions.　Copyright　©　2020　ASME.