In order to understand the factors influencing stand thinning in tropical natural secondary forests, aboveground biomass, species diversity and spatial patterns were quantitatively analyzed by using aboveground biomass model, diversity index and O ring statistics. Moreover, the effects of species diversity and spatial patterns on stand thinning were studied with thinning index calculated by Yoda selfthinning model. The results showed that stand aboveground biomass increased first, then decreased and increased finally with declining stand density. An inflection point of aboveground biomass change occurred at diameter class Ⅲ or Ⅳ, and this should be paid attention to during forest management. In general, there was no significant correlation between diversity index and stand thinning index. However, the medium value of species diversity index corresponded to the largest thinning index, suggesting that stand thinning was strongest with the medium species diversity. A significant negative linear correlation existed between largest aggregation intensity and thinning index as follows: α=-1.7873O₁₁(r)_max+2.3451 (R²=0.798, P=0.003). The results indicated that if plant population assembled excessively, stand thinning would be suppressed rather than promoted in the tropical evergreen monsoon elfin forest.