The　flexible　mode　of　operation　of　coal-fired　units　can　accommodate　large-scale　renewable　power　integration　into　the　grid,　providing　more　grid　capacity.　The　flexibility　transformation　of　coal-fired　units　in　thermal　power　plants　can　be　achieved　through　main　steam　extraction　and　reheated　steam　extraction.　A　300　MW　subcritical　unit,　600　MW　subcritical　unit　and　660　MW　ultra-supercritical　unit　with　six　flexible　operation　modes　were　chosen　as　the　research　model　to　investigate　the　thermal　adaptability　for　flexible　operation.　The　results　show　that　from　the　perspective　of　the　source　of　steam　extraction,　the　main　steam　extraction　scheme　is　suitable　for　the　flexible　adjustment　of　peak　load　capacity,　and　the　reheated　extraction　scheme　is　suitable　for　the　flexible　operation　of　low　load　and　high　thermal　efficiency.　Moreover,　from　the　perspective　of　thermal　performance　adaptability,　the　600　MW　unit　has　a　wider　load　regulation　capacity　than　the　300　MW　and　660　MW　units,　and　is　suitable　as　the　peak　shaving　unit.　This　work　can　provide　theoretical　guidance　for　different　types　of　coal-fired　units　in　choosing　flexible　operation　schemes.