Forest system in the upper reaches of the Yangtze River was chosen as the research object.The study area was divided in to 11 assessment units by the forest vegetation types.According to the index of canopy,litter and soil layer of different forest types and NOAA remote sensing in 2001 and field investigation,water resource conservation of forest ecosystem and its spatial distribution characteristics in the upper reaches of the Yangtze River were studied by the method of GIS.Results showed that mean comprehensive water conservation function of forest ecosystems was 79.33 mm and that of canopy,litter,and soil layer was 1.29,2.81 and 75.21 mm respectively.The total volume of comprehensive water resource conservation was1.667510¹⁰t and the water resource conservation of canopy,litter,and soil layer accounted for 1.63%,3.54% and 94.81% of the total volume.The soil layer was the main part of the total water resource conservation of forest ecosystems.The water conservation function of forest ecosystems firstly increased then decreased from the south to the north and decreased gradually from the west to the east,showing as curve and power function trend respectively.This change trend coincided with that of the soil layer and was contrary with that of the canopy layer.In the horizontal direction,the water conservation function of forest ecosystem presented the west high and east low spatial pattern.The border was the line of M in Mountain Chaping Mountain Jiajin Mountain Jinping Mountain Yulong Mountain.In the vertical direction,the forest water conservation increased gradually to altitude of 4200m,there after it declined.