Through the investigation of soil,topography,and vegetation in the forest lands of Miyun County,different site types are analyzed.According to the principle of key factors and the principle of practicality,evaluation,slope orientation,soil thickness and so on are selected as the key factors.Site types in the county are classified into 3 small site-type districts,9 site-type groups,and 15 site types and then the potential of accumulation is calculated.Moreover,the map of the site type classification is made by using GIS.It can provide a scientific reference for the allocation and plant management pattern of water conservation forests in Miyun County.