Based on the mechanism and basic equation of radiation and convection heat transfer,a heat transfer calculation model for superheater or reheater of once through boiler is put foward in the paper.With the model,the heat transfer on each tube can be examined and its characteristics are thus obtained.The effects of boiler construction,coal varieties,operating conditions and other factors on heat transfer are considered in this model.The heat transfer condition of superheater or reheater can be determinded in detail directly by the model,and a new method is provided for analying the problems of superheater or reheater,such as heat difference,film boiling,service life and so on.