The Sanjiang Plain region is one of the main marsh distribution regions in China,where marsh covers an area of 11200 km~2.The marsh formation resulted from the synthetic action of such natural factors as regional geological structure, geomorphology,composition of surface materials,climate,hydrology,etc.Most of marshes did not accumulate peat because of the restraint of regional natural conditions,such as big precipitation variability,smooth and shallow negative landform,etc.The peat marsh only developed at the ancient channel fed with groundwater,the middle and upper reaches of some marsh rivers and deep depressions. The peat of this region belongs to herb peat originated from water-body paludification,and its spatial distribution is unbalanced.The peat deposit in the plain area is characterized by a small quantity and abundant reserves,while the peat deposit in the mountain area is characterized b a great quantity and scarce reserves.There are big deposits with rich peat reserves in the eastern part of the plain and small ones with little peat reserves in the western part of the plain. The peatlands are chiefly distributed at negative lanaforms such as ancient channels,floodland,riverbed-floodland,valley depressions and thermokarst depressions.