Abstract: Under leading of the WTO market regulations, the reasonable exploration and sustainability utilization of Beijing mountainous resources were very vital to the mountain areas and the whole development of Beijing. Because of the varied topography of mountain areas, it was important to quantify and imitate the spatial heterogeneity of ecological factors in Beijing mountain areas. In this paper, 1∶50 000 scale DEM (digital elevation model) was built. Then the evaluation factors of slope, aspect etc were derived from DEM through the surface analysis function of Arcview software. Through the meteorological point data of this area, the sunshine duration, average yearly temperature and precipitation were modeled through DEM for the whole region. The results supplied the basic quantified ecological factors for fruit trees suitability evaluation, habitat simulation etc. On the other hand, with the help of the digital soil types map, soil texture map, soil depth map, soil pH map, geological type map of this area, the fuzzy sum method was used to evaluate the suitability ratings of fruit trees in this area through GIS. Seven fruit tree varieties with large market potential in Mentougou District were evaluated by this model. The acreage of these fruit trees except cherry was more than one thousand or even ten thousand hectares. On the basis of the actual land use data from remote sensing classification, compare the results with the current distribution of fruit trees, the shortcomings of the current distribution of fruit trees and potential of future development were analyzed, and then reference to the readjustment of current agricultural structure was supplied.