Abstract: A study on agricultural nonpoint source (AGNPS) pollution in Mianyang Guansihe watershed is conducted. The authors have developed a methodology to automatically produce a majority of input data required by an AGNPS model, and to display either all or selected AGNPS output data in GIS files. The specific steps are as follows: (1) data generating: using the remote sensing image processing system and some programs developed by the authors, the data required by the AGNPS model are generated from three sources, including the digital file with contour lines from topographic maps, the digital soil mapping units from soil surveys, and the land cover from landsat TM image classification; (2) data input: once the requires GIS files are generated, a computer program converts the GIS files into the tabular file format requires by AGNPS; (3) model output: all AGNPS output data are converted into GIS files, so that they can be used for further analyses.