| The Loess Plateau is a region where water and soil erosion is the most serious in china, especially, soil erosion is worsening and the regional ecological environment is deteriorating in loess hilly-gully region, which seriously hampered the harmonious development of social economy. Anjiagou watershed in Dingxi city of Gansu province was selected as research object in this thesis. Based on systemic hydrological and meteorological observation(1977～2008), and the information data of land use of 1987, 1997 and 2007, and relied on mathematical statistic and spatial analysis technology of GIS&Rs and so on, by the method of combining of qualitative description and quantitative analysis, the characteristics of hydrological factors such as rainfall, soil moisture, runoff and sediment in Anjiagou watershed were analyzed and summarized; Meanwhile, a suitable distributed hydrological model SWAT was constructed, that was used to simulate and study the coupling between variation of water and sediment and evolution of land use pattern, the dynamic variation law of water and sediment and land use pattern in Anjiagou watershed was further verified and summarized, and response mechanism that eco-hydrological processes on evolution of land use pattern was interpretated, that can provide theoretical foundation and decision basis for collocating optimally water and soil resources and improving the regional ecological environment of loess hilly-gully region in china.The main conclusions of this thesis were listed as following:(1)Rainfall was the main factors affecting variation of runoff and sediment in Anjiagou watershed, spatial and temporal distribution of rainfall was significant uneven. There was correlation between frequency of occurrence of different type rainstorm and yearly precipitation in watershed, but it was unscientific and biased that the level of storm frequency and the amount of runoff and sediment was directly determined by the amount of annual rainfall.(2)Annual rainfall impacted directly mean annual soil moisture content in Anjiagou watershed, precipitation was almost the only source of soil moisture, it was more, and soil moisture is greater. Soil moisture cycle of different land use types was "water compensation-water consumption-water compensation". There were differences in the vertical variation of soil moisture content of different land use types, and the greatest variation of soil moisture content distribution was in 0-40cm range of soil layer, it was a common feature of the profile distribution of soil moisture that amplitude of variation of soil moisture becomed smaller with the increase of soil layer depth. View from the function of regulate soil moisture, forest land was stronger than farmland and grassland. Water balance analysis of different land use types also showed that:Evapotranspiration of forest land was larger, its surface runoff was less relatively. So forest land can store runoff and increase infiltration of rainfall effectively, it was an important role in reducing soil erosion and storaging soil and water in Anjiagou watershed.(3)In loess hilly-gully region, situation of storage of water and sediment in slope land were changed by different land use types, there was a significant difference among annual runoff per unit area of five kinds of land use types slope lands, and it was same as annual sediment yield per unit area, but their mean trends in years were consistent, and were in accordance with the laws of "sloping farmland (Triticum aestivum L. cv Leguan)＞artificial grassland (Medicago sativa L.)＞arbor land (Pinus tabuliformis Carr.)＞natural grassland (Stipa bungeana Trin.)＞shrub land(Hippophae rhamnoides L.)"; under same land use type condition, annual runoff per unit area and annual sediment yield per unit area of slope lands were increased along with rising of the slope in research scale (10°～20°), and about slope lands of different slope degrees, there was no significant difference among annual runoff per unit area, but a significant difference existed among annual sediment yield per unit area.(4)A11 of land use types in Anjiagou watershed was disturbed by human in different degrees, the main feature of land use change was the area of forest land and terraced field were obviously increased, and farmland conversion and wasteland reclamation were their main source; the rate of transformation of terraced fields, sloped farmland and grassland were faster in 1997 to 2007 than that in 1987 to 1997, but various land use types in the landscape patch was balanced distribution trend in Anjiagou watershed.(5)According to the simulated results by SWAT model on Anjiagou watershed of yearly step, the simulated mean annually runoff had the best veracity, the veracity of simulated value in yearly step was better than that in monthly step. The veracity of monthly simulated value in rainy season was better than that in dry season, the simulated mean monthly sediment had not good veracity. SWAT model simulation results indicated:about runoff, the order of verage annual runoff per unit area of five kinds of land use types was cultivated land＞unused land＞grass land＞forest land＞other land(construction Land); about sediment, the order of verage annual sediment per unit area of five kinds of land use types was unused land＞cultivated land＞grass land＞other land＞forest land.(6)Numerical model scenarios were set up by using the method of fixed a factor(climate or land-use change), impact of evolution of land use pattern to variation of runoff and sediment were analyzed quantitativly. With the increase of vegetation cover, runoff and sediment in watershed were reduced, intensity of their variation response to change of vegetation cover were first strong and then weak, that is, when vegetation cover in watershed reached a certain value, its regulating effect to runoff and sediment would be reduced. Obviously, the ecological and hydrological functions of forest land and grass land were making runoff and sediment reduce, and the impact on sediment was greater than the impact on the runoff.
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