Abstract: Using TWINSPAN and CCA, we analyzed species composition and community structure of Quercus liaotungensis and Q. dentata-Q. acutissima mixed forests based on 43 plots from Mt. Dongling, Mt. Dahaituo and Labagoumen regions, Beijing area. Community structures of all the oak forests were simple but varied greatly in different communities. The results of TWINSPAN classification indicated that these 43 plots were clustered into 7 groups based on the flora composition of canopy layer.  CCA ordination demonstrated a significant relationship between Axis 1 and altitude, indicating the importance of temperature in determining community composition. On the other hand, Axis 2 showed significant correlation with aspect, which suggested humidity may play a key role in community assembly. The consistent results of classification and ordination emphasized the importance of environmental factors in shaping community structure and species composition. The species richness of these communities was low, which likely resulted from the  intensive human disturbance in this area.