In order to take into the full consideration all factors affecting ditch line selection, the great effect of 3S technologies on route selection was studied in this paper. By a brief introduction to 3S technology, the author discussed the establishment of control network by static GPS, mapping and locating by RTK, fast and conveniently obtained high-precision surveying data during preliminary survey and location survey of ditch line. Through composite processing of RS images, the author accurately and largely extracted the situations on hydrogeology, geographic information, local building materials and socioeconomic issues of irrigation area etc. along the route in the course of explorations and re-explorations. In the selection of ditch line, using GIS strong ability of data synthesis, geographical simulation and spatial analysis, the author extracted various thematic images via superimposed and composite processing of all kinds of information, got the optimum line by comparison and selection. The prospect on application of ditch line selection in the future is put forward according to development vision of 3S technology.