Using different succession types of Pinus tabuliformis plantation in the Beijing area as the research object, this study investigated the change rules and interaction of stand spatial structure, understory vegetation, and soil water of three different succession types:Pinus tabuliformis pure forests, Pine-Quercus mixed forests, and Quercus variabilis pure forests. The results were as follows. (1) There were significant differences in horizontal and vertical stand spatial structure, species diversity of herbaceous layer, saplings growth, and soil water physical properties among the three different succession types (P<0.05). In addition, the angle index, stand layer index and opening degree index of stand spatial structure parameters significantly affected the shrub and grass diversity of each type of stand (P<0.05), while the mingling degree, stand layer index and neighborhood comparison significantly affected the growth of saplings (P<0.05), and the mingling degree and stand layer index significantly affected the change of soil water (P<0.05). (2) The biomass of shrub and grass, saplings growth, and the physical condition of soil water were all the better within the mixed forest than in the pure forest and were mostly influenced by the mingling degree and the stand layer index. (3) The natural regeneration saplings of Quercus variabilis were observed in all succession types, with mixed forest having the most saplings and the best growth and the most intensive competition for forest resources. Therefore, interspecific relationships and forest resources can be regulated by adjusting the spatial structure of stand, so as to give full play to the functions and values of forest ecosystem.