The research of sloping farmland is the key part of soil and water loss harness as well as soil and water conservation planning, the development and the application of GIS offered a new technical means for the research of sloping farmland. It is the basic function for GIS to get unit polygon by overlaying the vector map, but the uncertainty of polygon is the disastrous factor affecting GIS's data quality. Based on MapGIS, updated information by DOM. The method of Overlaying Vector and Grid and operating attribute table is used to prosecute the sloping farmland investigation quickly in small watershed. It is the prominent of Overlaying Vector and Grid in the process of information combination.