Tree species diversity of a 40-yr-old secondary broadleaved forest which was destroyed by human cutting was invertigated for 18 sample plots (each 100 m^2) in Ailaoshan Nature Reserve, Yunnan Province. Measurements included species composition, tree height, diameter at breast height, and sprouting. The results revealed that the dominant species was Vaccinium duclouxii, and more than 2/3 of tree species and 72.7% of the total individuals (DBH≥3 cm) were regenerated by sprouting. Tree density in the forest decreased with the increases of height class and diameter class, whereas species abundance did not increase. Tree species diversity in the secondary forest was significantly lower than that in montane moist evergreen broadleaved forest at climax stage as compared by Shannon-wiener index, Simpson's diversity index, and Fisher's index.