A simple model interpreting vertical distribution of soil carbon was constructed and annual degradation rate constants of soil carbon for various forest soils were estimated. The model is based on the material balance at the soil surface, and assumes that the relationship between soil depth and soil carbon is linear. The estimated soil degradation rates were of the similar order of magnitude, and we concluded that this model might be used for rough estimation of soil carbon degradation rates of forest soils where vertical distributions of soil carbon are available.