Abstract: In 2005, in Mount Tianmu National Nature Reserve of Zhejiang, 9 subcompartments were selected in Phyllostachys edulis forest, and 36 sample plots were established around subcompartments for determination and analysis on mean DBH, tree height, crown density, forest age, density, species composition, slope, slope site, soil thickness and forest origin. In 2015, determinations were repeated. Principal component analysis on data of the 2 determination showed that the first principal component, including forest density, mean DBH, average height, crown density and species composition had contribution rate of 46.99%. The second principal component consisted of slope, slope site and soil thickness, had 20.26% contribution rate, indicating that site condition had lower effect than the first one on natural expansion of P. edulis. The third principal component was about the age and origin of forest, had the lowest effect. The analysis resulted that expansion of P. edulis was caused by simple structure and lower species diversity of neighboring forest.