In this study,the characteristics of TM images for Beijing study area are analyzed to find the spectral separability of TM’s bands for different objects,such as water,farmland,forest,grassland,concrete,cloud and shadow.An Normalized Difference Cloud Index(NDCI) is proposed to construct a simple decision tree mode with the Normalized Difference Vegetation Index(NDVI),Normalized Difference Built-up Index(NDBI),Modified Normalized Difference Water body Index(MNDWI) and slope.This model is then used to derive the information of ground objects,cloud and shadow,and the precision of results is evaluated subsequently.The areas of water body,forest,grassland and farmland are calculated under the support of GIS technology.Finally,the indexes of water body density and vegetation-cover in the autumn of 2005 in Beijing area are calculated.Results indicate that the selection of thresholds for this model is very simple and effective and the precision of model can satisfy the requirement to calculate the indexes of water body density and vegetation-cover.The results also indicate that the remote sensing technology can be used effectively in evaluating the quality of ecological meteorology.