Woody plants with its DBH≥1.5cm at a 160×160m shrubbery permanent forest plot at Tongguling National Nature Reserve in Wenchang, Hainan, have been investigated., and those plants have been classified into 7 size classes based on DBH to determine the regulation of Thinning. Results showed that: 1) Class Ⅰ (DBH<4.5cm) occupied a maximum percentage (64%). The community was "Inverse-J type", the order of stands density was young trees > small trees> grow-up trees,the community was in a stable state. It has a typical phenomenon of thinning caused by the self-thinning and alien-thinning which caused by the individuals to compete for more living space and resources. 2) Above ground biomass of each classes increased with the growth of density, in a small density range, above ground biomass increased swiftly with the growth of density, but changed slowly and tended to a constant value when the density tend to be 0.6 plant per square meter, and the power function equation was AGB=6×10⁷N^0.4626 or lnAGB=0.4626lnN+17.855. 3) It had a negative correlation between the density and the average DBH of each class (larger the density, smaller the average DBH) and its power function equation was:N=70.1d^-3.5506,R²=0.8808. 4) We simulated the sel-thinning law put forward by Yoda, and found that there was a significant coherence between stand density and average biomass, the correlation was: W=2219.1N^-0.5374 or lnW=7.7048-0.5374lnN, thinning index α value was 0.5374, it was largely differ from the 3/2 index put forward by Yoda,did not satisfy the-3/2 law of self-thinning. 5) 41 common species (individuals more than or equals 5 per 0.2hm²) and 51 rare species have been investigated. It has a certain discipline in terms of thinning of species of natural shrubbery.