Abstract: To study the rationality of density of landscaping trees in urban green space，we investigated the crown width and trunk diameter of 100 kinds of open-growing trees commonly used in landscaping. Data were analyzed using EXCEL and SPSS 23.0. results showed that the ratio of crown to diameter（ CW/D） did not correlate with the growth habits or branching of trees（ Coniferous and Broad Leaf Tree）. However，they were closely related to the shapes of canopy. Wide crowned trees（ e.g. umbrella-type，spherical，wide oval and wide pyramid） showed significant differences compared to narrow crowned tress（ long and narrow ovate，long tapered tower）and the Palmaceaes in terms of CW/D ratio（ P ≤ 0.01）. Trees with narrow crown had no significant difference in the CW/D ratio compared to Palmaceaes. The results suggests that:（ 1） For practical applications，the landscaping trees can be classified into 3 types according to the CW/D ratio，namely wide crowned，narrow crowned and palm-shaped trees. （2） Appropriate selection and allocation of trees by their shapes and CW/D ratio in landscaping and greening are beneficial to constructing reasonable flora structure. After green flora canopied，adjusting the density of flora with the reference of CW/D ratio is constructive to the growth of plants and proper utilization of space for maximizing ecological benefits.（3）For optimal ecological benefits，the recommended minimum intra-species spacing in the same canopy is defined as d1 = D×（CW/D） ÷100. Whereas the minimum inter-species spacing follows d2 = 1/2（CW）A +1/2 （CW）B.