Interspecific and intraspecific variations of plant functional traits help reveal plant adaptation strategies to the environment and to mechanism of community assembly. In this study, we investigated 4 key functional traits of 105 species and 4190 individuals to understand changes in woody plant functional traits of the Cyclobalanopsis glauca community in the karst area, Guilin city. These functional traits were leaf dry matter content (LDMC), leaf thickness (LT), specific leaf area (SLA), and wood density (WD). Combined with the variance decomposition method, we performed the mixed linear models to analyze the degree and proportion of interspecific and intraspecific variation of functional traits. Based on it, we used the null model method to detect the potential driving mechanism in community construction by considering or not considering the variability of intraspecific variation of functional traits. These results suggest that:(1) the variation of the four plant functional traits was dominated by interspecific variation, and the intraspecific variation cannot be ignored. (2) The nullmodel test shows that the environmental filtering test at the individual level is improved. Community assembly seems to affect traits on the scale of individuals. (3) For the Cyclobalanopsis glauca community in the karst area of Guilin city, environmental filtering is indeed an important driving mechanism for community assembly. Together with similarity restriction and random effects, it shapes the community construction with Cyclobalanopsis as the dominant species.