| The thesis analyzed the major plant community types, plant transpiration rates variety laws, soil water balance, precipitation, dynamic change of the regional desertification and the major influencing factors by the methods of field survey, remote sense analyze, located observation, and the major results is followed:1) Through field survey and remote sense analyze and located observation It is indicated that there are 11 plant commubity, the transpiration rate daily change precess curve of several major plants divide into single-peak, two-peak and single-two-peak three types, and a majority of plants monthly transpiration rate can reach to biggest peak. The bare lands and sand dunes where the soil water has hydraulic connection with underground water is likely to supply the soil water of 75 cm soil layers and the underground water. The annaul soil's evaporation has nothing with the annual precipitation during growing season under high-flow years.2) The water resources in Yanchi sand land can be divided into storm flood resources (groundwater resources), the forth shallow groundwater resources, water resource in bedrock faults, soil water resources and atmospheric water resources. The precipitation is the major source of the soil water resources and all kinds of water resources in the sand land. The interannuai change character of the precipitation in sand land is that, a drought year must occur in 1-2 years around a relatively highest-flow year. It is found that the average precipitation for every 7 years will take on a regular change. The average precipitation for every 7 years, which is described as y(mm) and the serial of the space, which is described as x(x>1,originated from the year of 1954) have such a relationship y=270+50sin[(x-1) π /3+π /2].The precipitation is small and the precipitation happen in the form of transient flood. The relationship between the annual depth of run-off, which is described as y(mra) and the annual precipitation, which is described as x(mm):y=0.0002x2-0.0385x+3.0409.It is found that the underground water resources and the area of the sand dunes are connected with annual precipitation. The exploitation of the underground water in low-flow years can reache to 23288 thousand m3. At this level, the area of sand dunes which collect the underground run-off should reach to 708.4km2 and it is 9.9 % of the total area of the Yanchi County.3) According to the different scale of the monitor and the evaluating the indicator system can be divided into two forms: macroscopic and microscopic indicator.The macroscopic indicator is the area of all kinds of sand dunes that can be measured by surveying method directly in a region.The microscopic indicator ascribed to the factors, which have close relationship with the quality of the land, For instance,the vegetation cover, the soil texture and the soil fertility and so on.therefore, we can use the area of all kinds of sand dunes as an indicator to reflect the degree of desertification when we make wind erosion desertification evaluation on a regional scale in Yanchi sand land.4) The formation and expand of the sand dunes of the Yanchi sand land is the result of the natural condition and human disturbance. The area of the sand dunes, which is described as A, the precipitation of the former year, which is described as P1, the area of cultivated land, which is described as M and the total amount of goats, which is described as N have such a relationship:A =-2.358P1+1.278M +48.1N-142.795.On the development level of the economics of today, when the exploitation of the underground water is ensured and the regional ecological environment is improved, the area of the sand dunes in low-flow years should be controlled to 15% of the total area of Yanchi County, which is possible and necessary,the ecological construction of Yanchi sand land should ensure that the area of the sand dunes is less than 1069.5 km2, at the same time, considering the size of cultivation and planting, the relationship between the total number of goats, which is descr...
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