The purpose of this study is to evaluate the hydrological impact due to temporal land cover change by gradual urbanization of Anseong-cheon Gongdo watershed ($371.8km^2$). Land covers of 1981, 1990, 2000 Landsat TM images were classified by maximum likelihood method. The watershed showed a trend that forest & paddy areas decreased about $33km^2$ and $27km^2$, respectively and urban area increased about $11km^2$ during the periods. To identify the impact of streamflow due to urbanization, WMS HEC-1 was used. According to apply Huffs quartile storm events by changing land cover data, peak runoff discharge of each frequency rainfall (50, 100, 500 years) increased about 56, 36, $192m^3/sec$, respectively.