水土流失是具有一定动能的流水将风化产物剥离原地,带到下游低洼处沉积的自然现象,它造成的后果是:(1)耕地资源减少,土地沙化,水土资源质量下降,旱涝等自然灾害频繁。(2)资源容量下降,生产条件艰苦,生产落后,人民生活贫困。(3)植被稀疏,生物种群稀少,生态环境严重恶化。水土流失不但影响山区生态环境和工农业生产的发展,制约着广大山区农村脱贫致富,而且影响到下游的防洪及人民生命财产的安全,影响着城市建设与发展,已成为我国经济社会可持续发展的重要制约因素,是我国的头号生态环境问题。 我国山区(山地、丘陵和崎岖的高原)面积约占国土面积的2/3,且我国地势高,坡度大。随着人口增加,许多坡地已被开垦成耕地。由于我国平原面积只占10%,随着国家战略中心向西移,及对粮畜产品的需求,人多地少的矛盾将更加突出。一些较陡的坡地也将成为开发的对象。坡耕地,由于是在不平坦而有坡度的土地上周而复始地耕作,对于水土的保护则如雪上加霜。哪怕是林草坡地,一旦开垦为农田之后,水土流失速度也会增至数十倍数百倍。由于航空摄影和卫星遥感技术相继发展,特别是当前“3S”技术和数字地球等高新技术蓬勃发展的形势下,如何进行水土流失治理就成为我们当前的历史任务。 地面坡度、坡向、高程是决定土地质量的重要因素，及时准确地提供它们的分布情况，对规划工作是非常有必要的。本文以ARCGIS软件为例，着重讨论在地理信息技术条件下，通过建立数字高程模型，进行地形地表分析，解决水土流失强度分类的问题进行讨论。

Soil erosion is a natural phenomenon that the kinetic energied water pushed the efflorescence result off where they are and took them aggrade. It takes the following effects:(1)the plantation resources reduced and the infield is sanded, the quality of water and soil are going down, natural-ties such as drought or excessive rain is in high frequency；(2)the quality of soil and water is declined; the people are in poor condition;(3)forest is getting smaller; the species of living things are lessened; the environment is getting serious. Soil-lost not only affects the development of the agriculture and industry, but also the safe of the people where they live lower reaches of a river. It is a critical factor to restrict the further social development and is the most important zoology environment problem in our country. The area of a mountainous area in our country is the two-third of the whole country area. With the people increasing, many sloping fields are becoming into plantation. Because of the western development and the requirement of the grain and livestock production, the contradiction between more people and less land is becoming acute. A lot of steep sloping fields are going to be the developing objects. Once they will be the cropland, soil erosion will turn into ten times or hundreds times. With the good development of the satellite remote sensing and air photography, especially the technique of “3s” and the digital-earth, it is the history task that how to deal with the soil-lost. Ground slope、aspect、elevation are the important factors to the land quantity. It is necessary for layout task that offer the surrounded situation of the factors mentioned above precisely in time. On the basis of ArcGIS, this paper discusses how to analysis the earth's surface，how to solve the classification problem of soil-lost through creating the digital elevation model in the geographical information technique condition.