| Loess plateau is one of the most severe zones of soil and water loss in the world, and its eco-environment is very weak, and it is the main sediment source area into the Yellow river. So, the main problem to the Loess plateau is the recovery of its vegetation ecology, the promotion of the sustainable development, and the decrease of the water and sediment disasters in the lower Yellow river. The recovery and building of the plant in the Loess plateau has an important and valuable sense for improving area eco-environment, promoting area economy and realizing the sustainable development of economy and society.In this paper, the Loess plateau is as the background, based on the typical study areas including Yan'an city's entourage and the east-one gully branched as the xi-zhao gully in the zhun-ge-er county, Inner Mongolia, one of the typical soft rock regions in the Loess plateau, the soil moisture property of the main plant type in the Loess plateau, the adjustment effects of the sea-buckthorn flexible dam on soil reservoir, and the sea-buckthorn flexible dam's eco-hydrology effects were analyzed by the method of combine of locating observation and field survey and indoor test analysis. Next, the purification effects of the vegetation fitter strip on non-point source pollutions were studied by the test. The merits and shortcomings of the three measuring water flow velocity through the sea-buckthorn flexible dam were compared, and the design parameters of the sea-buckthorn flexible dam were analyzed and discussed. Finally, the ecology benefits of small valley soil and water conservation projects were quantitatively calculated, and the contribution of ecology benefits to national economic evaluation was evaluated by the concerned theory and method of environment-economy subject and combining the two-stage world bank loan on Loess plateau soil and water conservation in bin county in shaanxi province. Achieved main study results and advances in this paper are as follows:(1) The soil water was gradually reduced in the succession course of the national plant from low stage to high stage, the soil water difference was not high and was at a high level at first returning farmland and herb community (Artemisia capillaries thumb and herb community) stage. In the middle succession stage, namely boscage stage, the soil water had an obvious variation, and the soil water was yet at a high level at first boscage stage, but the soil water had approached or attained it of arbor forest in the last boscage stage(corylus bosk). The plant succession course of from low stage to high stage was the consuming soil water stage of soil reservoir.(2) The sea-buckthorn flexible dam could formed deeper gully soil reservoir through alluvium, and the soil reservoir formed by the sea-buckthorn flexible dam had a big adjustment potential to gully soil water in the soft rock region, and that could provide and improve supply water condition for local plant grow and recovery.(3) Plant growth survey results showed that:â‘ the retarding and filtering effects of the VFS to surface runoff were closely concerned about the growth of herb community; and the sea-buckthorn was not fit as main species of VFS and it and herb community could not jointly be plant.â‘¡the sea-buckthorn is a kind of excellent plant for soil and water conservation and its growth is very good in shaanxi province, and it was suitably plant in the area between herb VFS and water body for receiving sewage, this can help stable riverbank and further improve the runoff filtering performance.(4) Small district runoff simulation test results showed that:the VFS could effectively filter the SS(suspended solid), N(nitrogen), P(phosphor), and COD in runoff, and the average reducing rate of it to the four kinds pollution load was over 70%; the density, height and rigidity of plant had a marked effect for the purity performance of VFS, and grass filter strip formed by developed herb community had a better filtering effect.(5) By the three methods of PIV technique, buoy and dyed-tracer, water flow velocity in the sea-buckthorn flexible dam was respectively measured, and test data were theoretical analyzed and compared based on test results. The test results observed by dyed-traced was close to that observed by PIV, test results observed by buoy were different from that observed by PIV, and the buoy method was rougher result for man-made factors. PIV technique was more practical than dyed-tracer and buoy techniques in test veracity, practices arid effects.(6) In small watershed, the sea-buckthorn flexible dam's design was subject to rainfall, underlying surface, terrain and natural conditions etc. The primary design idea was suggested that the sea-buckthorn flexible dam plant parameters were make from watershed design rainstorm and flood together with gully form, and the plant parameters of sea-buckthorn flexible dam were valuably discussed from theory based on the basic theory of project hydrology.(7) Employed environment-economy theory and methods, by the shadow price method, it was quantitatively calculated and analyzed for vegetation conserving and improving soil and water, fixing carbon and supplying oxygen and maintaining landscaping effect. On the basis, ecology benefit was brought into national economic evaluation of soil and water conservation projects. The construction productions and invest benefits of soil and water conservation projects were evaluated and it was obtained that soil and water conservation had very significant ecological benefits.
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