Abstract: To provide accurate base map for the field investigation and to ensure the smooth implementation of the first national soil and water conservation survey.They were studied that the determine of the exact location for soil and water conservation unit in the different scale topographic maps and how to accurately decide and describe boundary.The results showed that： according to the framing code standard of the topographic maps,it was easily maked the framing relationship chart between the four kinds of map（1∶100000,1∶50000,1∶25000 and 1∶10000）.Combined the framing code with this chart,the accurate position of 1∶10000 topographic map could be quickly determined on the 1∶50000 and 1∶25000 topographic maps,then the water conservation survey unit was very conveniently detemined on the basis of the work procedure standard of the first national soil and water conservation survey and the 1∶10000 topographic map.The key to describe unit boundary was how to accurately find ridge line,it needed to find the highest point of the investigation unit on the topographic map,then to describe boundary along the biggest curvature part of the contours from the highest point,according to the elevation gradually reduce characteristics of the ridge line.