The process of conversion from wetland into cropland(CWC) is the main feature of land cover change in Sanjiang plain in the past 50 years.Natural eco-environment has been destroyed seriously because lots of wetland was substituted by cropland.This paper analyzed spatial-temporal characteristics of landscape gradient of wetland and cropland based on RS and GIS,during 1954~2005 period, taking Bielahong basin as case study area.Data using in this paper was acquired with topographical data and remote sensing data such as Landsat MSS,Landsat TM,CBERS.Results showed that,in 1954,most of the study area was with high wetland landscape gradient.Only the area in southwest part nearing Songhua River and area in upriver zone of Nongjiang River were covered by dense wetland.However,in 2005,most of the study area was covered by cropland.In study area,changes of spatial distribution cropland landscape and wetland landscape revealed spatial laws of conversion from wetland into cropland.This phenomenon can be summarized as the enlargement of croplands towards east and the shrinkage of wetlands towards northeast.