1998年以来中国在生态环境脆弱区实施了一系列生态建设工程，为了评估工程的效益，监测工程实施地区的生态环境变化趋势，在生态脆弱区选择了具有代表意义的5个典型区，采用遥感与地理信息系统技术结合的方法，对这些地区在1997-2002年5年内的生态环境变化进行了动态监测。监测结果表明，这5年来，退耕还林还草、天然林保护、防护林建设和小流域治理等生态环境建设工程已经取得较大进展，各治理区的环境正在逐渐改善。

In order to combatthe developingtrendof eco-environmentdegradation, a seriesofnational environmental projects\nhave been carried out in frail ecological zone since 1998. The construction measures adopted by the projects include handing\nfarmland backto forestland orgrass land, protecting nature forestry fromdeforestation, planting sheltering forest, conserving soil\nandwater, and so on. To evaluate the effect of the projects on eco-environment, five sites in different eco-environmental\nzoneswere selected as study areas to monitor the change of land cover over 1997—2002. Through analyzing the change of land\ncover, it suggests that as a result of national environmental projects, the eco-environment is rehabilitating gradually except for\nthe study area of East-northern China. The sheltering forestry has increased 1479 hm2, farmland has increased, and forestland\nand grassland decreased in the region of the case site located in East-northern China. In the region of the case site located in\nthe north of Beijing, the total area resulted fromthe construction project is 51492 hm2, farmland has decreased, and forestland\nand grassland have increased. In the region ofthe case site in the north part of Shanxi Province, the total area resulted fromthe\nconstruction project is 11115 hm2, farmland has decreased, and forestland and grassland have increased. In the region of the\ncasesite located in the middle part of Gansu Province, the total area resulted from the construction project is 17437 hm2,\nfarmland has decreased, and forestland andgrassland have increased. Inthe regionofthe case site inSichuanProvince, thetotal\narea resulted fromthe construction project is 65347 hm2, forestland has increased, and farmland and grassland have decreased.