Nuclear reactor severe accidents can lead to the release of a large amount of radioactive material and cause immense disaster to the environment. Based on a heat conduction model, the DEBRIS-HT program for analyzing the heat transfer characteristics of a debris bed after a severe accident of a sodium-cooled fast reactor was developed. The basic methodology of the DEBRIS-HT program is to simplify the complex energy transfer process in the debris bed to a simple heat transfer problem by solving the equivalent thermal conductivity in different situations. In this paper, the models of the DEBRIS-HT code are explained in detail. The comparison between the simulation and experimental results shows that the DEBRIS-HT program can correctly estimate the heat transfer process in the debris bed. In addition, the DEBRIS-HT code is applied to model the core catcher of the China fast reactor. The calculated dryout heat flux of the postulated accident, in which 100% of core melts and drops on the core catcher, agrees well with the prediction result of the Lipinski’s zero-dimensional model. And the error between them is about 10%. The calculated dependence of dryout heat flux on particle size is also in good consistence with the prediction by Lipinski’s zero-dimensional model. Then, the temperature distribution and the temperature excursion of the debris bed during a likely accident are analyzed, which provides significant reference to the severe accident analysis.