The effects of different planting densities (1000, 500, 250stem/hm2) on growth increment of juvenile and mature wood were studied in Populus×xiaohei. The result indicated that the juvenile period was about 12～13 years and there are no differences in juvenile wood growth rings at different planting densities. The effects of planting densities on widths and basal area of juvenile and mature wood were highly significant. An obvious tendency of increasing juvenile wood width and basal area with decreasing planting densities was seen. The highest mature wood growth increment was found at the planting density of 500stem/hm2. The percentage of juvenile wood area ranged from 74% to 83% depending on different planting densities. The highest juvenile wood proportion being at the lowest planting density. The growth rate of juvenile wood was about 10 times higher than that of mature wood. There were remarkable differences in the growth rate of both juvenile and mature wood at different planting densities. It’s concluded that planting densities showed various degrees of impact on the growth of juvenile and mature wood, and juvenile wood was more susceptible to planting density.