Research on the ash deposition characteristics of tower boilers is carried out from the aspects of structural parameters, flue gas flow rate, and burning coal quality of the heating surface, for an ash collapsing accident in 1000 MW double-reheat tower type boiler. The causes and hazards of the heating surface ash deposition is also analyzes，and the reasons for the change of furnace pressure during the process of ash collapsing is explained. Measures to avoid serious ash deposition were put forward when the boiler heating surface operates in the low load， which can avoid frequent occurrence of ash collapsing accidents. It is of reference to the operation of the same type of boiler.