Taking a 1000MW ultrasupercritical doublereheat updraft boiler an example, it considers from the structure arrangement of the heating surface, the flow rate of flue gas, the concentration of fly ash etc. It explores the main cause of ash deposition on the heating surface, and studies the reasons for ash sloughing. The countermeasures are put forward to guarantee the stable and safe operation of boilers.

1000MW unit, ultrasupercritical unit；doublereheat, updraft boiler, ash deposition, ash sloughing, countermeasures