Abstract: The effect of different stand density to poplar crown structure and the relation between crown structure and poplar canker under different density were analyzed.The results showed that the difference of the firstorder branch diameter and canopy layer density was significant among 15 plots. Disease index was significant positive correlated with stand density(0.631) and significantly negatively correlated with crown shape ratio(-0.540). Besides, the results of path analysis showed that the general effect of all of crown structure indexes were negative, and their order was crown width, total leaf area, percentage of crown length with height, leaf area index, height under branch, crown surface area, canopy layer density, firstorder branch diameter, crown shape ratio and firstorder branch angle. The negative general effect of total leaf area and crown width was the largest. Accordingly，the choice of crown structure indexes of densitycontrol of poplar canker should emphasize crown width and total leaf area. Density (planting spacing was 2.0 m×3.0 m) of the first stand among 5 stands was optimum, and disease state of poplar canker was the lowest.