Abstract:The mehtods of contrat reseach and analysis of measured information about precipitation,runoff and silt discharge were employed to study the function of the silt arrester dams to detain silt in Wangmao valley as an example.Results showed that the fanction was very significant.Compared with before harmess,modulus of silt discharge decreased from 1800t/km2 to 504t/km2,being97%.The target of no silt running out of the valiey was almost reached.