Based on remote sensing and GIS technology,the authors analyzed two-way succession processes of natural and man-made wetlands and impacts of natural environmental features on the processes in Sanjiang Plain during 1986-2005.Results showed that two-way succession processes of wetland in Sanjiang Plain were characterized with mutual transformation between marsh and paddy field from 1986 to 2005.During the periods of 1986-1995,1995-2000 and 2000-2005,ratios of transformation area from marsh to paddy field to total area of transformed marsh were 7.61%,37.99% and 28.81%,respectively,while ratios of transformation area from paddy field to marsh to total area of transformed paddy field were 4.83%,13.69% and 4.84% respectively.Main natural environmental features in relation to two-way succession between marsh and paddy field in Sanjiang Plain were characterized by being the regions of meadow soil and marsh soil,elevation of 0-100 m,slope gradient of 0-1°,physiognomies of low flood plain,high flood plain,depression and first terrace.