Based on data from 34 plots of the middle part of Qinling Mountains in Shaanxi Province,the ecological gradients of the plant communities were studied by the methods of TWINSPAN and DCCA,in terms of the interactions between plant species and communities and topographical factors.The results indicate that:(1)34 plots record 297 species vascular plants,belong to 77 families 178 genera.Among those,72 families Angiospermae plants,2 families Gymnospermae plants,and 3 families Pteridphyta plants.The wide distribution species include Pinaceae,Fagaceae,Rosaceae,Compositae,Gramineae,and Liliaceae.(2)Based on TWINSPAN,34 plots were classified into 13 associations,and the number of associations which dominant species are Pinus tabulaeformis+Quercus aliena var.accuteserrata,possessed about 40% of the total number,is the widely distributed mixed type of the study area.(3) The first of DCCA ordination axes indicates the altitude and slope position gradients,and the second of that indicates the aspect and slope gradients.The correlation coefficients of elevation,slope and DCCA one and two axis arrived the most values,respectively (-0.946 2,-0.795 7).The main factors restricting distribution of the communities are altitude and slope in this area.(4)The DCCA ordination of dominant species and samples simultaneously reflect the topography gradients of pine and oak mixed forest communities in this area.