1998年的特大洪水灾害，以及2000年京津地区的沙尘暴，使得中国政府对生态环境的建设更加重视。为了改善中国的生态环境，就需要恢复植被，一些耕地就需要退耕还林还草。哪些耕地需要退耕还林还草，这些耕地在空间上的分布情况如何？为此，探讨了利用地理信息系统技术确定需要退耕还林还草耕地的数量及其空间分布。包括4个步骤。首先，建立土地利用、土壤侵蚀、数字高程、坡度、坡向、植被指数、降雨和温度等数据库，并对生态环境质量进行评价，从而得到生态环境质量数据库；其次，从土地利用数据库中提取旱地的数据，并与坡度数据、土壤侵蚀数据、植被指数数据和生态环境质量数据进行叠加分析；再次，确定退耕还林还草的原则，并在GIS的支持下，确定需要退耕还林还草的面积及其空间分布；最后，利用降雨数据进一步分别确定退耕还林或还草的面积及其空间分布。该研究结果可以为中国的生态环境建设提供科学的决策依据。

Natural disaster such as the large flood took palce in 1998 in China and the dust storm in 2000 around Beijing makes our government paying more attention to improve the ecological environment in China. In order to improve the ecological environment, a great deal of the dry land must be returned back to forest or grass land. Where the dry land must be changed inlo the forestland or grassland is a very important question.In our study GIS is used to find the place where the dry land must be changed into forestland or grassland. In includes four steps. Firstly, the database is extablished including land use database, soil erosion database,DEM, slope database, aspect database, normalization vegetation index (NDVI) database, precipitation database and temperature database. The ecological environment quality database is oltained thtough evaluating the ecological environment quality. Secondly, the dry land from Landuse database was overlain with slope database, soil erosion database, normalization vegetation index(NDVI) database and the ecological environment quality database. The distribution of the dry land of different slope was analyzed. The distribution of the dry land of different slope under different soil erosion, different NDVI and different ecological environment quality was also analyzed. Thirdly, the expert knowledge about the dry land was collected, and a model of finding suitable places for changing into forestland or grassland is formulated on the basis of the knowledge. Finally, the suitable places are overlain with the precipitation layer to decide where trees need to be planted or where grass need to be planted. It shows that the results provide an important scientific decision base for government to construct the ecological environment in China.