Based on remote sensing technique，using 1990's Landsat TM data and 2000's Landsat ETM data，the authors conducts the comparative study of mainstream area of Songhua River by means of human-computer interaction method． The results show that the area of Songhua River mainstream was 738 102 km2 in 1990， and was 810. 451 km2 in 2000． From 1990 to 2000，the increased area of river mainstream is up to 72. 349 km2 due to soil erosion and water loss． Meanwhile，the dynamic changes of surrounding vegetation cover are also studied． It is estimated that the trend of surrounding soil erosion and water loss of Songhua River mainstream becomes worse in Jilin Province．