Abstract: This study investigated the Rhodoleia championii Hook. f. + Castanopsis fordii Hance community, a representative subtropical forest in Nankun Mountain, Longmen County, Guangdong Province. Quadrat-based surveys, coupled with the variance ratio method (VR) and Fisher’s exact test, were employed to assess species diversity and interspecific associations. Results revealed that: (1) The community exhibited high species diversity, with a relatively even distribution of species in the tree layer, whereas the shrub layer contained a greater number of species but exhibited uneven distribution, leading to a lower diversity index; (2) The overall interspecific associations within the community were significantly positive, suggesting a stable community structure. In the tree layer, one highly significant positive association pair, five significant positive association pairs, and two significant negative association pairs were identified; (3) Based on population clustering, interspecific connectivity, and ecological habits, the 14 dominant populations were classified into four ecological species groups. Species within the same group exhibited similar ecological adaptations and resource requirements, generally displaying positive associations, while species from different groups predominantly exhibited negative associations. These findings provide a theoretical basis for the conservation and management of natural secondary forests in Nankun Mountain.