Abstract: The Quercus aliena var. acuteserrata community is a typical representative of deciduous broad-leaved forests in the southern foothills of the Funiu Mountains. Therefore, understanding its species diversity and relationship with environmental variables is crucial for forest management in this region. From August to September 2019, 32 plots of 20 m × 20 m were established to systematically investigate the species composition, diversity, and environmental variables across tree, shrub, and herb layers. One-way ANOVA was used to analyze differences in species diversity among layers, and redundancy analysis (RDA) was applied to explore the influence of environmental variables on species diversity in each layer. The results showed: (1) A total of 146 plant species were recorded across the 32 plots. The tree layer had the fewest species (33), with Q. aliena var. acuteserrata dominating overwhelmingly (importance value: 70.25%). The shrub layer had the most species (74), including 29 tree seedlings, while the herb layer had 64 species but exhibited significantly retarded development, with an average herb cover of only 1.74%. (2) ANOVA revealed significant differences in diversity indices among layers (P<0.05), ranked as: overall diversity > shrub layer > herb layer > tree layer. (3) Environmental drivers showed distinct layer-specific effects. Higher elevations and greater soil total potassium enhanced overall community diversity. Tree species richness was favored by higher elevations, abundant soil potassium, thicker litter layers, acidic soils, and lower phosphorus availability. Shrub diversity increased with elevation, while herb diversity correlated with higher soil total phosphorus. The driving mechanisms of species diversity vary across different layers in the Q. aliena var. acuteserrata community in the southern foothills of the Funiu Mountains. Therefore, biodiversity conservation and management strategies should fully account for the feedback mechanisms of species across these different layers.