Abstract: In order to providing a theoretical basis for precision improvement of artificial forest quality, a 10-year-old Pinus armandii plantation in western Sichuan was chosen as the research object, to explore the effects of different thinning intensities (thinning retention of 1800, 1350, and 900 trees per hectare) on the species composition, bio-diversity, and vegetation structure of understory plants, and soil nutrients three years after thinning in this area. The results showed that: (1) The thinning technique was useful for understory plant diversity There are more types and quantities of understory plants with the greater the intensity of thinning.Pioneer plants are light loving plants; (2) The diversity index of understory plants increased with the increase of thinning intensity. Pielou index, Margalef index, Shannon-Wiener index, and Simpson index all showed significant differences between thinning intensities and CK (P<0.05). Margalef index and Shannon Wiener index are significant differences in M1, M3 (P<0.05); (3) The cover of understory plants showed significant differences between the thinning treatments and CK (P<0.05), and there was also significant difference between M1 and M3. (4) There was significant difference in soil organic matter content between thinnings and control (P<0.05), and showing a significant difference in M3 thinning intensity and M1& M2 (P<0.05). Soil organic matter content was also significantly positively correlated with plant diversity indexs (P<0.05). The results of short term study indicates that a reserve intensity of 900-1350 trees per hectare is favorable from the enhancing the understory plants diversity and soil nutrient of Huashan pine plantation.