Five indices were applied to analyze the species diversity of Fagus longipetiolata community in Leigong Mountain,and based on the investigation data of 2 quadrats,tree size class method was applied to analyze the structures of the dominant populations,.and t-test of v/rn ratio, mean crowing index, negative binomial parameter, patchiness index and Morisita index were applied to analyze the spatial distribution patterns of two dominant populations. The result expresses that the species diversity of tree layer and fruticose stratum is relatively lower,while the herb layer relatively higher. However,the result of integrating the tree layer and fruticose stratum and herb layers indicates that the total species diversity(indicated by species richness) of F. longipetiolata community is still higher. In the spatial distribution pattern,that F. longipetiolata population,the individual percentage of Y trees accounted for 52.0% in Q1 and 49.1% in Qz and 49.4% in Q3,The I class has none,The Ⅱ less,for the decline population. However,the population in Cyclobalanopsis glauca The 1V has more,the I, V are more than F. longipetiolata population on the individual quantity. The spatial distribution patterns of the two dominant populations are distributed in clumps, but the diversity exists in clumping degrees. With the increase of the size classes, the population of F. longipetiolata transits from random distribution to clumping distribution, while the population of C. glauca from clumping distribution to random distribution.