Operational　flexibility　improvement　of　coal-fired　power　plants　has　become　a　priority　objective　with　the　high　penetration　of　renewable　energy　sources.　The　regulating　measures　applied　frequently　in　improving　the　operational　flexibility　indeed　affect　the　exergy　efficiency　of　coal-fired　power　units　during　transient　processes.　In　this　study,　the　exergy　efficiency　evaluation　of　operational　flexibility　measures　during　primary　frequency　control　processes　was　focused　on,　and　the　exergy　analysis　methods　of　the　thermal　system　were　used　on　the　basis　of　the　second　law　of　thermodynamics　to　analyze　the　mechanisms　for　improving　the　flexibility　at　four　regulation　measures,　and　the　exergy　storage　conversion　efficiency　and　exergy　destruction　accumulation　were　quantitatively　compared.　It　turns　out　that:　among　the　throttling　extraction　steam　of　high-pressure　heaters,　feedwater　bypass　of　high-pressure　heaters,　and　condensate　water　decrease　of　low-pressure　heaters　measures,　the　exergy　storage　conversion　efficiency　and　the　exergy　destruction　accumulation　increase　with　the　regulating　time　of　primary　frequency　control.　The　measure　of　throttling　extraction　steam　of　high-pressure　heaters　is　the　most　potential　option　for　improving　operational　flexibility,　with　maximum　value　of　the　maximal　output　power　increment　and　maximal　exergy　storage　change　rate　of　71.11MW　and　-89.84　MW,　respectively.　With　respect　to　the　economy,　the　measure　of　throttling　extraction　steam　of　low-pressure　heaters　is　the　best　option　due　to　its　smallest　exergy　destruction　accumulation　among　all　the　measures.　This　study　provides　a　detailed　guidance　for　the　selection　of　the　optimal　regulating　measures　when　considering　the　enhancement　of　exergy　efficiency　and　flexibility　comprehensively　under　different　conditions　and　periods.