Abstract: The eco environmental condition in Longyangxia reservoir area is worse and worse in recent years.This place is in the high arid and semi-arid region in Qinghai-Xizang Plateau,it is one of desertified development areas in our country.The desertification was intensified by irrational economic activities,such as reclaiming,animal husbandry.The desertification occurs in most of grassland.The sustainable development and stability of society is affected by severe desertification.Based on the remote sensing information with multi-temporal(1987,1996),multi-spectral as well as investigation in spot,dynamic monitoring of desertification is worked out with GIS,in which some softwares,such as IDRISI,ARC/INFO,ARCVIEW and so on,and PⅡ microcomputer act as main tools and equipment.Supported by this system,through a series function of GIS,such as attributive items adding,updating,spatial analysis and so on,being operated,the dynamic information of desertification and corresponding maps are obtained in Longyangxia reservoir area from 1987 to 1996,therefore,dynamic monitoring of desertification is carried out.The results show that desertification has much characteristics in this area,which include:firstly,the area of all kinds of desertified land is 8 236.78 km² in 1996,it accounts for 71.5% of total area of this region,among which the very severe,severe,on going and potential desertified land are respectively 10.9%,1.3%,10.3% and 49%.The very severe desertified land has been increased purely 189.11 km² in nine years from 1987 to 1996 in Longyangxia reservoir area.The average spreading rate of desertification is 21 km² per year.Secondly,although the desertified land has been reversed in some areas,the positive course of desertification trends to be intensified,in which the on going and very severe desertified land play an important role,it indicates that the rate of desertification is very quick.The grasslands as well as ecological environment of this area have been degrading seriously,it will become our main task to control this state.Thirdly,although natural factors play an important role for the desertification,the irrational economic activities are not neglect factors that has intensified desertification.

Key words: Longyangxia reservoir area, desertification, remote sensing, geographic information system