Consisting　of　steam　cooler,　condensation　zone　and　drain　cooler,　the　three-stage　feedwater　heater　is　widely　used　in　the　thermal　power　plants.　To　study　the　variable　condition　characteristics　of　three-stage　feedwater　heater　with　water　level　controlled,　a　GSE　simulation　model　of　that　in　300MW　thermal　system　of　power　plant　was　established.　Validated　by　the　steady　states　of　the　heater,　different　dynamic　characteristics　were　investigated　when　the　load　varied.　The　results　revealed　that　the　steam　pressure,　feedwater　flow　and　feedwater　inlet　temperature　drops　would　have　a　significant　influence　on　the　extracting　steam　flow,　feedwater　temperature　increment　and　terminal　temperature　difference.　The　dynamic　trends　were　intensified　with　the　variation　of　the　input　condition　enhanced.　The　response　time　of　extracting　steam　pressure　drops　is　430s　and　that　of　feedwater　flow　drops　would　be　prolonged　to　600s.　The　dynamic　processes　with　water　level　controlled　were　carried　out　and　showed　that　adjusting　flow　valve　could　keep　the　water　level　stable　and　secure　the　operation　of　heater　smooth　and　steady.　However,　frequently　controlling　the　position　of　flow　valve　could　impair　the　steady　procedures　of　other　parameters　and　prolonged　the　response　time.　©　2015　The　Japan　Society　of　Mechanical　Engineers.