On the basis of our recent experimental data and previous works by other investigators, the CHF model has been developed. It is the first model, which can predict the spatial variation of CHF along the flat surface facing downward. The physical framework established by Cheung and Haddad (1997) has been kept in the present modeling. The prediction showed that the most upstream region over the inclined heater surface is mostly susceptible to occurrence of boiling crisis. The present work is expected to contribute to the accurate estimation on the cooling limit of the ex-vessel core catcher cooling channel.