The estimation model of the evaporation from a forest floor was constructed in this study. This model consisted of the sub-models to calculate the evaporation rate from a mineral soil surface proposed by Campbell and to estimate the two effects caused by the cover of a litter layer. The one is to decrease the evaporation rate from a mineral soil layer. The other is that a part of precipitation is stored in it and evaporates. These effects were expressed with the simple equations based on the experiments. The litter layer decreased the evaporation rate from the mineral soil layer to be around 30%. The evaporation rate from the litter layer was calculated from the solar radiation and the water content volume of the litter. This model was verified in the forested water basin. The calculation with this model showed that the annual evaporation rate from the forest floor was around 127mm, 57mm and 70mm, annually, summer and winter, respectively. These corresponded to shares of 17%, 12% and 29% in total evapotranspiration in this basin.