For the assessment of the level of stream pollution, SWAT -WASP model linked with GIS was applied to a representative rural watershed and evaluated for its applicability through calibration and verification using observed data. Using daily water yields, sediment yields and nutrient discharge simulated by SWAT model, WASP input file was build. Point source pollutant and water quality change in stream was considered in WASP model. For the model application, digital maps were constructed for watershed boundary, land-use, soil series, digital elevation, and topographic data of Bok-Ha watershed using GHASS. The model application results showed that the simulated runoff was in a good agreement with the observed data and indicated reasonable applicability of the model.