Abstract: Based on the 3S technology and the soil erosion equation revised by us,the soil loss amount and areas to be harnessed in the upstream of Longchuanjiang River of the Yangtze River were numericaly simulated and quantitatively analyzed.The calculated results are as following:(1) The soil erosion amount in 1998(drought year) was 840069.19 t,the erosion area was 2293.7841 km²,the soil erosion amount in 1999(water-logged year) was 8 90 182.6 t,the erosion area was 2 293.784 1 km²,the sum of the strong,heavy and violent erosion areas in 1999 were obviously stronger than that of 1998.(2) Soil erosion area over middle degree in 1999 was 35.2% of total area,meanwhile it was 26.0% in 1998.(3) The areas to be managed rapidly in classification sizes of prevention strength in 1999 and 1998 respectively occupied 16.27% and 14.63% of the watershed area.(4) The modeled results are similar to the observation value on the spot,which indicats that the method can be applied to soil erosion research of the red earth and monsoon region of Southwest China and it is accurate,convenient and practical.