Abstract: We surveyed crown structure of poplar and disease state of poplar canker in different site conditions，and analyzed the effects of site conditions on crown structure and the relation of crown structure with disease state of poplar canker. The results showed that crown surface area(CSA) had very significantly positive correlations with soil types, thickness of soil layer and humus layer; and total leaf area(TLA) had a significantly positive correlation only with soil types. The correlation of crown width(W) with soil types and thickness of humus layer respectively was very significantly positive and significantly positive; the correlation of height under branch(Hub) with thickness of soil layer and humus layer respectively was very significantly positive and significantly positive. Besides, disease state of poplar canker and crown structure were very closely related. Disease index was very significantly, negatively correlated with W, percentage of crown length with height(PLCH) and CSA, and was significantly, negatively correlated with TLA. The order of positive direct effect of crown structure indices on disease index was LAI, CSR, W, TLA and Dfb, and the order of negative direct effect of crown structure indices on disease index was PLCH, CLD, CSA, Hub and Afb. But from decision coefficient, the order of the significance of crown structure indices to disease index was LAI, CLD, PLCH, W, CSR, TLA, Hub and Dfb. Considering comprehensively the relation of crown structure indices with site condition, crown width should be considered as the major index of crown structure for site control of poplar canker because of the moderate significance of crown width to disease index of poplar canker, the significantly positive correlation of crown width with site condition and the very negative correlation of crown width with disease index of poplar canker. So the measures of the choice of better planting site(loam, thick soil layer and humus layer) or fertilization can be taken to regulate crown width for controlling the disease state of poplar canker under a low level and to keep the ecological balance and the stabilization of economic benefit of poplar forests.