To evaluate the influence and importance of woody plants’ distribution and species composition in urban parks on the plant diversity of urban green space ecosystems, the woody plant communities in Taiping Mountain Park and its surrounding small parks in Qingdao City were studied. The variance decomposition method of the bivariate richness of plant communities investigated the contribution of species to β Diversity (SCBD) and plots to β diversity (LCBD). The relative importance of single species, families, plant types, and parks to β diversity was further analyzed. The main results: The influence of single species on β diversity was related to its occurrence in different parks. The dominant tree species with a high frequency of occurrence and the weak tree species with a low frequency of occurrence had lower contributions to β diversity. The most frequent tree species, such as Celtis sinensis, Zelkova serrata, and Pistacia chinensis, contributed most to β diversity. The dominant families in the woody plant community, such as Rosaceae, Cupressaceae, Pinaceae, and Sapindaceous, made essential contributions to β diversity, and their species composition and specialism were higher than other families. Deciduous broad-leaved tree species dominated the woody plant groups in Qingdao urban park. Overall, the SCDB values of deciduous plants were higher than those of evergreen plants, and those of broad-leaved plants were higher than those of coniferous plants. However, at the individual level, the average SCBD value of deciduous trees was lower than that of evergreen trees, and that of broad-leaved trees was lower than that of coniferous trees. Although the species richness of evergreen or conifer plants was lower, the species uniqueness of evergreen or conifer plants was higher, and they had higher conservation value. The contribution of Zhongshan Park to β diversity was the largest, and the LCBD values were positively correlated with the species richness of the park. This study suggests that parks with high species richness should be protected, and using environmental heterogeneity in different parks to increase the uniqueness of woody plants is of great value in preserving the plant diversity of urban green space.