Abstract: In order to choose the appropriate species to improve and optimize the pioneer communities in Southwest China karst area, a pot experiment was conducted to test the effects of Vitex negundo on seedlings of Cyclobalanopsis glauca and Delavaya toxocarpa under the Vitex negundo canopy with different moisture conditions. The results indicated that relative growth rate of ground diameter and plant height of C. glauca and D. toxocarpa increased with soil moisture conditions. The relative growth rate of seedling under canopy of V. negundo was always lower than the open sites in the same water condition, and the difference increased with the soil moisture. SPAD of C. glauca in open site had no obvious changes in all moisture conditions, but increased with soil moisture under canopy of V. negundo. SPAD of D. toxocarpa in the open site increased with soil moisture, but showed no differences under canopy of V. negundo. SPAD of C. glauca and D. toxocarpa in the open site was always higher than under canopy of V. negundo in the same moisture condition. Relative neighbor effect of C. glauca and D. toxocarpa was negative in all moisture conditions and increased with soil moisture. The pioneer shrub V. negundo inhibited the growth of C. glauca and D. toxocarpa seedlings under canopy of V. negundo, and the inhibiting effect increased with soil moisture.