Using the methods of combining landscape ecology with GIS spatial analysis, this paperanalyses the dynamics of the marsh landscape structure of the Sanjiang Plain in the past 20 years,furthermore, taking Fujin County, located in the north of the plain, as an example, analyzes theconversion between marsh and other land use types. It is shown that the marsh in the Sanjiang Plaindecreased greatly in the past 20 years, but the trend has begun to reverse. The marsh area decreasedby 51.33% from 1980 to 1996, whereas it decreased by 4.19% from 1996 to 2000. Thefragmentation of the marsh increased; the number of the patches increased by 326 from 1986 to1996, whereas it only increased by 18 patches from 1996 to 2000. It is obvious that the speed ofpatches number diminished and the marsh fragmentation decreased, which shows that the reclamationof the marsh converted from the fragmentation to the brim in a large area of the marsh. Thereclaimed marsh has mainly converted to paddy field and dry land. Large-scale reclamation in theSanjiang Plain influences its natural environment directly: the climate of the region turns from coldand wet to warm and dry, which makes the marsh both in the low-temperature northem part and inthe deeply stagnant eastern part suitable for further agricultural development.