According to erosion vertical zone distribution in the loess hilly and gully region,the methods for demarcating distribution slope location of soil erosion patterns at small watershed are put forward.Based on erosion environmental characters in the loess hilly and gully region,the framework of the distributed water erosion prediction model at small watershed supported by GIS is designed.The fundamental erosion processes in this model included splash detachment,sheet flow detachment and deposition,rill flow detachment and deposition,ephemeral gully flow detachment and deposition,gully flow detachment and deposition,and channel flow detachment and deposition.Meanwhile,the calculation processes of this model are discussed in detail.In term of the principle of dynamic balance of mass,the calculation of sediment yield in the whole watershed is accomplished.