| Soil erosion is now regarded as a global environment problem, which gets more and more attention from all people in the world. Serious soil causes many the eco-environment problems, such as water shortage, flood disaster, deterioration of water environmental and so on. Clean water and cultivable lands have become the most important strategic resource in 21st century, water and soil is the foundation of the life. It's the shared responsibility of all the people in the world to protect soil and water resources.Beijing , with a total area of 16,410 km~2, locates in the north part of North China Plain. Us mountain area is 10,072km~2, accounts for 62% of the total area. Mountain area is the main conservation area of the water, the main resort for the capital people.The soil in the mountain area is very thin and the slope is very deep. The degree of the slope more than 25° accounts for 40% of the whole mountain area, and the soil layer less than 30cm accounts for over 50%. According to remote sensing survey of soil erosion in 2000, the soil erosion area of the whole city is 4,089km~2. Soil erosion and water loss lead to the land productivity decreasing, eco-environment exacerbating and water pollution, and further aggravates the water shortage problem in Beijing. So soil and water conservation is the basic guarantee for economic sustainable development in Beijing mountains area.Set out from practice, Beijing put forward an idea of soil and water conservation that takes water resource protection as a center, according to the law of soil erosion to build the Three Conservation Belts: ecological restoration, ecological management and ecological protection, finally to construct ecological-clean small watershed. So we need a technology and a tool to quantitatively evaluate the rules of soil loss and sediment transport for Beijing, to investigate the status, scale and development trend of soil erosion, determine the best land harness and management program, reduce or try to avoid land degradation, provide a scientific basis for soil and water conservation and eco- environment construction, and a decision-making basis for government to make decision.Soil erosion prediction model and soil loss equation are now the quantitatively evaluation tool to investigate soil erosion status. It is very important to set up a soil loss equation suitable for the Beijing mountainous area by referring to soil erosion prediction models out-seas which are relatively perfect and widely-use and combining with thepractice observation data in Beijing. According to the research ,we find out the physical model is still in the research phase because the parameters relatively more and difficult to get, while the empirical model has more practicability as it could be established only depending on a large number of observation and statistics data. So we choose the most mature and widely used experience mode, the USLA general soil loss equation, as the basic model frame for the Beijing mountains soil loss equation.The slop soil loss observation was stared in 1987 in Beijing, and the slope runoff plots were completed and improved in 2000, the entire seven mountain districts (counties) have emplaced the slop runoff stations. According to use the field observation date of the rainfall, runoff and sediment content in 127 runoff plots and almost 1000 slope runoff fields, artificial rainfall test data of more than 60 times, rainfall process data of 2894 times of 10 hydrometric stations and daily rainfall data of 24 hydrometric stations, and all these data are 25 years from 1980-2004, summarizing the research results both of overseas and domestic, this paper research the calculation methods or the parameter value of all the soil loss factors of soil loss equation suitable for the Beijing area,find and make sure the calculation methods or the calculation value of factors the of Beijing mountain soil loss equation, which are rainfall erosion force factor R, soil erosion possibility factor K, slope length and grade factor SL, vegetation cover and manage factor C, soil and water conservation measures factor P.The researcher also find that in the rocky mountains the soil surface often has a lot of gravel (mineral particles with diameter larger than 2mm ), according to field observation data and artificial rainfall tests, we find that the soil erosion decreases with the increase of gravel coverage. So in the Beijing soil loss equation, adds the gravel cover factor (R_F )as an independent factor, according to artificial rainfall tests to educe the relationship between soil erosion and gravel coverage, and at last put forward the soil loss equationA = RKLSCPR_F which suitable for Beijing mountains. By using the observation data of slope runoff stations, the definite coefficient of this mode is 0.974; the calculated result is very near to the observed value, which proves that both the soil loss equation and the paramcter value are reasonable.Taking this soil loss equation as technology tool, applying both sample survey and grid investigation methods to implement large scale soil erosion status investigation in Beijing has received some initial results. In the bulletin of Beijing Soil Loss Monitoring from 2004 to 2006, combining this soil loss equation with rainfall data of 123 rainfall station all over the city to draw up a rainfall erosivity contour map, according to the distribution of rainfall erosivity and by using the observation data of the 7 slope runoff stations all over the city to calculate the slope soil loss of the whole city, which greatly enhance the veracity and science of the bulletin.We will continue to do the observation in the slope runoff stations in Beijing, using the observation data with long years to revise the parameter and improve the mode, and go onto do the further research on the mode application, especially on the aspects of soil loss forecast and soil and water conservation plan, provide service for the land and water resource management, soil loss prevention and ecological construction of Beijing mountains.
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