Abstract: The 50 years’development and construction leads to the great reduce of wetland area, the whole function degradation of wetland and a series of serious ecological environment problems in the Sanjiang Plain.The Sanjiang Plain evolving from development to conservation is an inevitable choice for the sustainable development of socio-economy and environment.On the basis of re-recognization of wetland importance in the Sanjiang Plain, the implementation of returning farmland to wetland project can recover integrity, naturalness and diversity of regional ecosystem, improve its fragile ecological environment, and make contribution for ecological environment improvement of China and the whole world.This paper chooses the Sanjiang Plain as research object, discusses the feasibility of using the remote sensing and GIS technologies to determine the farmland number and spatial distribution of returning farmland to wetland.Four steps are included.Firstly, the GIS database platforms for making decisions are established including land use, DEM, wetland buffer, river buffer, lake buffer, administrative area, soil types, geomorphological types and farmland productivity which are created by remote sensing and GIS technologies.All data are referenced to the same projection and coordination and interpolated as grid data with a resolution of 100 m.Secondly, the low yield farmland data from farmland productivity is overlain with river buffer data, wetland buffer data, elevation data and lake buffer data.Thirdly, the expert knowledge about returning farmland to wetland is collected, and the models for finding a suitable place for being returned back to wetland are formulated based on ARCGIS.There are 525 652 ha and 194 029 ha of farmland to be gradually converted into wetland on the basis of the models, which respectively accounted for 8.76% and 3.23% of the farmland in 2005.Finally, the distribution of the place suitable for wetland in administrative area is obtained by using the overlay and spatial statistic analysis.The research shows that, with this method, considerable manpower, material and financial resources can be saved.The result can not only be presented in table form, but also in graphic form, which is very useful for planning, executing and managing the returning farmland to wetland and provides scientific basis for ecological environment establishment in the Sanjiang Plain.