Abstract: Taking forest resources in the mountainous area of Beijing as the researching object, spatial distribution, resources utilization and adaptive capacity to environment of the eight dominant forests were studied by applying niche analysis.Environmental factors of forest, such as precipitation, sunshine, cumulative temperature and soil quality, were partitioned to five resources gradients.Based on geographic information systems, spatial databases were built for the distribution information of dominant forests and resources gradients of environmental factors.Niche breadths and niche overlaps of eight dominant forests growing on the five gradients of different resources dimensions in the mountainous area of Beijing were measured using Levins and Smith’s indexes and Pianka’s method.The results show that resources availability influences niche matrices greatly.Niche breadths calculated by Smith’s formula which considers resources availability and distribution indicate the capacities of resources utilization and environmental adaptation effectively.Niche overlap between two forests with broad niche breadth is usually great.The average niche overlaps among dominant forests in the study area are widely high, which indicates that the eight dominant forests require similar environmental conditions and resources sharing.