Abstract: Scale effect is of fundamental ecological significance to exploration of structural variation and dynamics of plant communities. As the Wuyishan preserves certain patches of natural primary forest ecosystems typical of the central subtropics, exploration was carried out in that region of mechanisms of the formation and maintenance of the species diversity, and spatial distribution of the species diversity index in the region and its scale effects. Based on trees ≥1 cm in DBH within the forest dynamics monitoring zone, 9.6 hm² in area on the Wuyishan, Fujian Province, Simpson index, Shannon-Wiener index and Pielou's evenness index were calculated using seven sampling scales (5 m×3 m, 10 m×6 m, 20 m×12 m, 40 m×24 m, 80 m×48 m, 133.3 m×80 m, 200 m×120 m). Variance and coefficient of variation was used to describe spatial variability, as well as relationships between these indices and sampling scale. Results show that all the indices are related with scale, and feature significantly regional distribution. In addition, species diversity is not only related to spatial scale, and its distribution also follows the rule of scale deduction. Therefore, in analyzing species diversity of plant communities in future, attention should be paid to the rule of scale deduction and spatial variability brought about by sampling scale and areas.