Functional diversity of a plant community, which is based on plants traits, has been proposed as a key component predicting ecosystem function. Studying the difference between plant functional diversity at community level and environmental factors along with the sloped (shady-sunny) gradient is helpful to explore the process of plant community and the mechanism of community construction. In this study, we caculated four functional diversity indexes including functional richness (FRic), functional evenness (FEve), functional dispersion (FDis), functional divergence (FDiv) based on two plant functional traits (i.e. specific leaf area, SLA and wood density, WD) and three environmental factors (rock exposure rate: RER, soil total phosphorus: TP, and soil available phosphorus: AP) in typical Cyclobalanopsis glauca communities and examined the correlation between changes in this relationship and slope gradient in the Karst hills of Guilin. Experiments were carried out at 14 sampling points with gradients sloping from the middle area of the hills to the foot of the hills (shady-sunny). In total, 14 plots (20 m×20 m) were sampled. Individuals of tree with DBH ≥1 were identified, and two plant functional traits of these plants and three soil environmental factors of each plot were measured. Then we calculated four functional diversity indexes based on two SLA and WD. Next we preformed non-parametric Wilcoxon signed rank test to assess differences in the four plant functional diversity indexes and in three environmental factors along the slope gradient. Based on the results of this analysis, we used multiple stepwise regression analysis to determine the key soil factors controlling variation in plant functional diversity indexes at the community in relation to slope gradient. We observed that: (1) the functional richness, functional evenness, functional dispersion, and functional divergence in shady areas of the slope were significantly greater than those in sunny areas of the slope. (2) Rock exposure rate and soil available phosphorus in sunny areas of the slope were significantly greater than those in shady areas of the slope, whereas soil total phosphorus in shady areas of the slope was significantly greater than that in sunny areas of the slope. (3) Multiple regression analyses of functional diversity and environmental factors indicated that the functional dispersion and functional divergence were significantly negatively correlated with rock exposure rate on shady slopes, but the correlation was not significantly on sunny slopes. The functional evenness was significantly negatively correlated with soil total phosphorus and the functional divergence was significantly negatively correlated with soil available phosphorus in sunny areas of the slope, but the correlation was not significantly on shady slopes.