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The environmental information system is a thematic analysis subsystem in the water redistribution management system for the Tarim River Basin.This paper studies mainly the general design,structure and functions of the thematic analysis subsystem and the integration with other subsystems.Firstly,the ecological quality indices(EQI),such as the biological abundance index,vegetation coverage index,hydrographic net density index,land degradation index and pollution load index,are used to investigate the environmental quality in the Tarim River Basin.Secondly,a quota method is put forward for calculating the ecological water demand of natural vegetation.Thirdly,some indexes including the ecological degeneration index,risk degree index and regeneration degree index are calculated based on the concept of ecological risk assessment and the method of landscape ecology,and the corresponding ecological risk is analyzed and assessed.The results show that it is of the obvious practicality and maneuverability to take the means of ArcGIS+Oracle9i+ArcSDE to develop the environmental information system.The study results can be used to carry out the thematic assessment and analysis of ecological environment in arid areas,and can also be referred in developing other systems concerned.