GIS technique was applied for ffie work of water supply protection, and GIS rnaps were produced by this technique in Cheong-ju area. They are actual runoff rnap and regional groundwater protection map. The digital database was estabilished for creation of these maps in EGIS(Environmental Geologic information system). A lot of environmental, hydrological and geotedmical data relating to the area were collected from various sources, and used along with the results of the field investigation and laboratorv works in the interpretation of environmental geologic characteristics of the area. These special maps can be applied in the establishment of water supply protection and regional land use planning. For instant, the actaal runoff rnap is very linportant for hydrologic study, and groundwater protection map for susceptibility to groundwater contamination in the area. Actual runoff of the study area was calculated about 148mm using the method of SCS(Soil Consrevation Service) in GIS. The GIS technique was effective in watershed analysis and water balance study.