The present invention discloses a 3S technology based method for returning farmland to forests. The method comprises the following steps: determining a returning farmland to forest scheme through remote sensing and GIS monitoring; generating a DEM by digitizing contour lines, and performing overlay analysis on an elevation map, a slope map, an aspect map, a land use map, and a map of returned farmland, to obtain a database of land use, slopes, and aspects; grading soil erosion by using a USLE equation; grading soil fertility and land productivity; performing overlay analysis on the database of land use, slopes, and aspects, soil erosion grading data and land productivity grading data, to obtain a grading and distribution map of returning farmland to forests; performing comprehensive analysis to obtain a planning map for returning farmland to forests; and digitizing collected data, to build a database for returning farmland to forests. The method disclosed by the invention is adapts to local conditions, and is suitable for trees and lands, and the human and capital investment is reduced, so as to meet the requirements for rapid returning farmland to forests and sustainable development.