Taking upstream watershed of Qingshui river as an example, the typical watershed in western mountainous area of Beijing City, Geographic Information System(GIS) and SCS(Soil Conservation Service) were used to estimate the collectable rainwater resource of different land-use types from June to August in different hydrological frequency years, which are dry year, normal year, and wet year.In addition, the SCS-CN computed runoff data and the observed data which were selected from 10 times rainfall during June to August in 2008-2009, were used to analyze the errors and to test the accuracy of SCS-CN. The results showed that:(1) The collectable rainwater resource calculated from June to August in different hydrological frequency years were 7.16×10⁷ m³,10.36×10⁷ m³ and 5.71×10⁷ m³, respectively, accounted for the average percentage of 82.43%;(2) The percentage which rainwater resource of different land-use type collected from June to August in normal year were as following:lawn and woodland accounted for 86.13%, farmland and garden plot accounted for 4.87%, industrial and mining warehouse land, residential and other land use types accounted for 9%, respectively;(3) Comparing the computed runoff data with observed data, the acceptability was 90%.