In this paper, we studied the influence of anthropogenic disturbances (thinning management) on the species diversity of understory plants in Pinus koreansis plantations in eastern Liaoning province. Investigations were conducted by establishing sample\|plot in the experimental sites (20 m×30 m). Production of trees was estimated by measuring tree height, DBH and canopy width in the experimental sites under different thinning intensities. Diversity of understory vegetation was surveyed by sample plots method in Spring (the middle ten-day in May) and Summer (the last ten-day in July). Two sample plots (1m×10m) were established in each experimental site along the hillside for surveying the plant species, height, abundance and coverage. Based on the calculations of α-diversity such as Simpson index (SP), Shannon-Wiener index (SW) and Pielou index (PI), we analyzed the species diversity of understory plants in Pinus koreansis plantations. The results showed that anthropogenic disturbances had altered the understory light conditions, improved the growth of vegetation, and impacted obviously the species diversity of higher vascular plants. The more the disturbance density enhanced, the more plant species and quantity increased. There were 24 times species in all of the thinned plantations more than those of in the control plantations. The richness and diversity of plant species were significantly higher in Pinus koreansis plantations with different disturbances than those in the control plantations. Anthropogenic disturbances changed the composition of understory plants, and the mutual plant species increased with the disturbance intensity enhanced. In addition, both the mutual plant species and analogical coefficient in disturbance plots were higher than those of the control plots. Overall, the results suggested that anthropogenic disturbances not only improved the biodiversity of understory plants, but kept on the forest ecological benefits (e.g., water conservation), and possibly promoted positive succession of Pinus koreansis forests as well.