Abstract: In order to monitor and evaluate the ecological environment quality (EEQ),this study established an EEQ assessment model based on the ecological factors including vegetation coverage index,bare-soil index and slope that were derived from MODIS data and DEM data.Taking Wuding River Basin (WRB) as the study area,which is located in the arid and semi-arid region with a fragile ecological environment,this model was then employed to monitor and evaluate the EEQ of WRB from 2000 to 2016 on both spatial and temporal dimensions.The results of the study demonstrated that overall the EEQ of this basin in recent 16 years has been showing an improving trend with the proportion of high EEQ areas accounting for 7.56% in 2016.However,there are yet some regions,including Shenmu County,Jia County,Hengshan County and Dingbian County of Yunlin City,where serious environmental pollution existed due to a rapid local economic development.There was a decreasing trend of EEQ from southeast to northwest in the basin,which is generally consistent with the basin's natural geographic characteristics.In the southeast of the basin,the water and heat conditions are relatively good,which is beneficial to growth of plants and thus causes high quality of ecological environment.The distribution of yellow soil and grassland shrubs that are easily eroded makes the EEQ in the southwest of the basin moderate to good.Besides,it was also found that the improvement of EEQ has a close relationship with the soil and water conservation projects in the basin.The main constraint of EEQ improvement is its fragile ecological environment and limited level of economic development.The method proposed in this study can monitor quickly and timely the EEQ variation in areas of large scale and thus serve the purpose of providing support for ecological environment protection and improvement.

Key words: ecological environment quality, watershed protection, ecological factor