Community can be regard as a complex system which is built with different connecting species. Exploring the pattern of the structure is the basis of system modeling, which contributes to our understanding of the system property and the relationship between structure and function of the system. Complex network theory has been used in studying food webs and mutualistic networks, but the use of network theory in describing the pattern of forest plant diversity hasn't been tested. In this study, using the network theory, we analyzed the network structure of species diversity pattern of woody, shrub, and herb in a warm temperate deciduous broad-leaved forest of Dongling Mountain, Beijing. The results showed that the pattern of species co-occurrence is non-random, showed an so called "small world" pattern. The co-occurrence species networks of herb, shrub and wood are significant different. The net work for herb is looser, it has longer average path length than the shrub and wood layer. These results indicate that the network theory is useful in analyzing the diversity pattern of different layers of species among associated communities.