In this study,leaves of thirteen common ornamental trees were collected form sampling sites with different pollution degrees in Yan’ an Municipality to determine the sulfur content in leaves using BaSO₄ turbidimetry and spectrophotometer.One-way ANOVA analysis,average contaminative Index analysis were used to examine the absorption capacity of SO₂ for Yan’an ornamental trees.The leaf anatomical structure of the thirteen species of ornamental trees from three sampling sites were observed with paraffin sectioning method and nail oil seal.The twelve anatomical indices were analyzed.Through the methods of principal components analysis and path coefficients analysis to evaluate how the leaf anatomical structure influence the SO₂-absorption capacity.The results showed that:(1)with different pollution conditions,the SO₂ absorption capacities of different species were significant difference,and the SO₂ absorption capacity of same species in different pollution conditions were significant difference either.The order of average sulfur absorption capability of thirteen ornamental tree species in Yan’an was:Salix matsudana(2.64)＞Salix babylonica(2.28)＞Amygdalus persica var.duplex (2.20)＞Amygdalus persica(2.15)＞Prunus cerasifera cv.pissardii(1.95)＞Sophora japonica(1.73)＞Sophora japonica cv.pendula(1.67)＞Buxus sinica(1.57)＞Syringa oblata(1.41).Berberis thunbergii cv.atropurpurea(1.41)＞Ailanthus altissima(1.30)＞Fraxinus chinensis(1.28)＞Ligustrum vicaryi(1.27).(2)The twelve anatomical indices(thickness of leaves,thickness of upper epidermis,thickness of lower epidermis,cuticle thickness of upper epidermis,cuticle thickness of lower epidermis,thickness of palisade tissue,thickness of spongy tissue,thickness ratio of palisade tissue to spongy tissue,compactness of leaf structure,stoma density of lower epidermis,stoma length of lower epidermis,stoma width of lower epidermis) had significant differences among thirteen species of ornamental trees,and had higher sensitivity.(3)Through the methods of principal components analysis,the accommodation of former four components has reached 87.875%,which picked six indices with larger contribution rate (compactness of leaf structure,cuticle thickness of upper epidermis,cuticle thickness of lower epidermis,stoma density of lower epidermis,stoma length of lower epidermis,stoma width of lower epidermis);Cuticle thickness of upper epidermis,compactness of leaf structure,stoma width of lower epidermis;through the path coefficients analysis,the three indices,thickness of upper epidermis,compactness of leaf structure and stoma width of lower epidermis have great direct impact on SO₂-absorption capacity(their direct path coefficient are 0.92,1.49 and 0.65,respectively) and weak impact on indirect impact on SO₂-absorption capacity.Instead,the other indices,thickness of lower epidermis and stoma density of lower epidermis,stoma length of lower epidermis,have large impact on SO₂- absorption capacity.Those six anatomical indices could be the indices to evaluate SO₂-absorption capacity comprehensively.