Abstract: The 22-year-old Pinus armandii plantation in Jinshajiang river basin was selected as the research object, and three gradients of canopy density of 0.5, 0.7 and 0.9 were formed by thinning and pruning. The species composition and diversity of shrubs and herbs under different canopy density stands were studied. The results showed that: (1) The number of plant species decreased with the increase of canopy density. Elsholtzia rugulosa Rhododendron parvifolium, Pteris cretica, Rubus foceanus, and Diplazium donianum were the dominant plants in 0.5, 0.7 and 0.9 canopy density respectively, but their important values did not exceed 0.21. In general, the proportion of high bud plants was the highest, and with the increase of canopy density, the life forms with the largest proportion were underground bud, high bud and ground bud plants. (2) The richness index, Simpson index and Shannon Wiener index of understory plants with different canopy density were significantly different, all of which decreased with the increase of canopy density. The canopy degrees of 0.5 and 0.7 were significantly higher than that of 0.9. The evenness index of understory plants was not significant, and the distribution of shrub plants was relatively uniform. (3) There were the most common species in 0.5 and 0.7 canopy density. The similarity coefficient of 0.7 canopy density and other canopy density was higher than 65%, and the community structure of the understory vegetation was relatively stable.