Abstract: Taking a 660 MW ultra-supercritical circulating fluidized bed (CFB) boiler as the research object, the calculation model of flow and heat transfer on heating surfaces under power failure condition was established, and a calculating program for the transient characteristics of heating surfaces was developed based on Fortran language. Variation laws of working medium and tube wall temperature at the outlet of heating surfaces were calculated when the heat storage of metal tube wall was considered under power failure condition. Results show that the boiler equipped with an emergency water supply pump with a pressure of 35 MPa and a water delivery capacity of 140 t/h can ensure the wall temperature safety of heating surfaces. The results are of great significance for the selection of emergency water supply pump and the treatment of these conditions in (ultra) supercritical CFB boilers with the external bed.