Abstract
In recent years, the eco-environment in the upstream of the Yellow River has been degrading due to both the global changes and the sharper contraction between human and nature. The eco-environmental problems such as grassland degeneration, sandy desertification and water erosion have seriously affected on the regional economical sustainable development. In order to protect and recovery the eco-environment in the upstream of the Yellow River, it is important to dynamically detect eco-environment with remote sensing and GIS. The region around Longyanxia reservoir is chosen as a study site, which is one of the most seriously eco-environmental degrading regions in the upstream of the Yellow River. the eco-environmental detection information system in this area is established by the remote sensing technology integrated with GIS. Based on the analysis of the multi-temporal and multi-spectral Landsat TM date with GIS, the eco-environmental changes are detected dynamically from 1987 to 1996. The result shows as manifested bellow:

1. the sandy desertified land has been increased and kept a sustainable developing situation. The sandy desertified lands accounts for 71.5% of total study area, among which the very severe, severe, on going and potential sandy desertified lands are respectively 10.9%, 1.3%, 10.3% and 49%. The sandy desertified is getting more severe from 1987 to 1996. the average spreading rate of the very severe sandy desertified land is 21km2 per year from 1987 to 1996.
2. The very severe and severe water erosion are mainly distributed in this area. The water erosion is one of the most serious eco-environmental problems in this area. The serious water erosion not only affects the regional eco-environment, but also endangers the security of Longyanxia reservoir.
3. The land is mainly used for animal husbandry and rainfed agriculture, which are dependent on the primary productivity. The structure of land use is unitary and unreasonable, the grassland is degraded seriously from 1987 to 1996, which results in the desertificating and the decline of the land productivity.

So it is necessary and urgent to combat desertification and protect eco-environment in the upstream of the Yellow River.

1. Introduction
The upstream of the Yellow River is located in the northeastern Qinghai-Xizang plateau with a high altitude and cold weather. Under the high coldness, arid and semi-arid geographical environment, the fragile eco-environment is formed in this area. In recent years, the climate has been warming up and drying affected by the global changes. Due to the climate changes and the regional sharper contraction between human and nature, the eco-environment has been degrading all along, which resulted both in the serious eco-environment problems such as grassland degeneration sand desertification and water erosion and the regional economical sustainable development. In order to protect and build the eco-environment in the upstream of the Yellow River, it is important to investigate, assess the status of eco-environment and detect the changes of eco-environment dynamically. So we have carried out a project on the dynamically detecting of eco-environment in the upstream of the Yellow River and chosen the region around Longyanxia reservoir as a study site.

Longyanxia reservoir now is the largest water conservancy project built in the upstream of the Yellow River. The region around the occupies about 11500km2 and is within the coordinates of latitude 360, -360, 27' N and longitude 1010 -1010 31' E, Which is in the transitional zone between steppe and desert steppe. The climate is characterized by low, highly variable temperature and rainfall, high wind speed and frequency, high evaporation losses. The mean annual summer temperatures range from 120 C to 200 C and the mean annual winter temperatures drop to -120 C. the mean annual rainfall varies from 311-402 mm. The region has dominantly textured sandy soils which generally have low inherent fertility status, poor water holding capacity and low in organic matters. Due to fragile eco-environment as well as injudicious use and the overexploitation of natural resources, hectares of pastures have become highly degraded, which has distributed the ecological balance and as a consequences the sandy desertification spreads quickly and water erosion has intensified. The region has become one of areas where the eco-environment has been seriously degrading in the upstream of the Yellow River.