| The resources of soil and water are the most valuable natural resources and the crucial base of human being. With the rapid increasing of population and the intensity of exploiting natural resources in the world, it becomes a essential problem that the loss of soil and water is a grate harmfulness to the sustainable development of the region. Every country pay attention to the conservation of soil and water and the suitable harness of soil and water resources after World War II. Three Gorge Area form Chong-qing to San-dou-ping of Yi-chang was the most important region in the upper reaches of Chang-jiang river where the loss of water and soil was urgently needed to be harnessed. The situation of the loss of water and soil not only affected Three Gorge Dam, but also affected the sustainable development of the middle and upper reaches of Chang-jiang, even the whole watershed of Chang-jiang. Presently, whether in the synthetically utilizing and developing or in the restoring and rebuilding of degraded eco-system, the basic scale was small watershed and the small watershed was justified to be reasonable spatial scale in mountain area. The 5 aspects of the loss of water and soil and regulating eco-environment were discussed based on the study of YuZiGou small watershed and San-he ecological orchard. The method and model of predicting and assessing the loss of water and soil was built and the model of regulating eco-environment in order to suitably harness the resource of water and soil in Three Gorge Area. 1 The assessment on the danger of soil erosion of watershed in Three Gorge AreaThe method of dividing assessed units on the danger of soil erosion was inquiredand the danger of soil erosion appraised in San-he ecological orchard, Feng-du county ?Chong-qing province by means of Analytical Hierarchy Process and System Cluster supported by the software of ARC/INFO 8.0.2 and SPSS 10.0. The factors affecting the danger of soil erosion were considered in an all-round way and the limitation and indistinction was avoided during the process of assessment. Results showed that the danger of soil erosion was mainly subject to the three factors of slope, the thickness of soil and the degree of plant cover and the area of the dangerous type, the more dangerous type and the seriously dangerous type was 57.49% of the area of the entire orchard. Because of the danger of soil erosion , it was not suitable that the excessively economical woods was planted and it was reasonable that the economical woods and the ecological woods were paid equal attention during the process of "planting woods after withdrawing cultivated land" in the ecological orchard. 2 Prediction of the loss of water and soil of small watershed in Three Gorge AreaThe relation between the loss of water and soil and the loss of nutriment was formulated by means of simulated rainfall and observing runoff of small region. Results showed that the nutriment was mainly related to the runoff of the tiny particulate matter in soil and the nutriment which run off with runoff was subsidiary. Compared with the violet soil, the nutriment which run off with runoff had greater proportion in the whole loss of nutriment in yellow soil and it was not negligible because it was mainly soluble nutriment. The method of supplying Geographical Information System" ARC/INFO to predict soil erosion amount of watershed was probed in this paper. Based on the field survey, the geographical data base of YuZiGou small watershed was built and the method of calculating the value of factors of USLE was studied. By the support of ARC/INFO Geographical Information System and integration of GIS and USLE, the soil erosion amount of YuZiGou small watershed was predicted. Results showed that the annual average soil erosion amount was 3893.38t/km2 and it belonged to middle degree erosion in YuZiGou small watershed; but the erosion amount of sloping land whose area accounted for 29.48% of the total area accounted for 81.98% of the total soil erosion amount of YuZiGou small watershed; the annual averag...
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