Abstract:Based on data of 30 plots from Huanglong Mts. in Northern Shaanxi, Quercus liaotungensis communities(QLC) were classified into six associations by clustering method, namely A. Quercus liaotungensis-Spiraea pubescens；B. Q. liaotungensis-Ostryopsis davidiana；C. Q. liaotungensis-Lespedeza bicolor；D. Q. liaotungensis—Cotoneaster multtflorus；E. Q. liaotungensis-Sophora viciifolia；F. Q. liaotungensis-Rosa hugonis. Additionally, calculation of the species diversity of different QLC and QLC on different slopes indicates that Whittaker diversity indices differentiate obviously among communities and relate closely with their habitats, especially the slope exposure , N>NW>ES>WS>S. Calculation and analysis of niche breadth and niche overlaps of the species in arbor and shrub layers of QLC show that in arbor layer, Quercus liaotungensis, Pinus tabulaeformis and Betula platyphylla are not only bigger in niche breadth (LB 1.2-1.5)but also are greater in niche overlap（Oik 0.7-0.9）, and that strong competition exist among them in current succession stage; in shrub layer, the niche breadths of Spiraea pubescens,Corylus heterophylla, Atermisia sacrorum, Rosa hugonis are bigger (LB>1) than others, but that of Lonicera ferdinandii, Celastrus orbiculatus,Rhamnus davurica, Smilax stans is smaller (LB 0.4-0.45).The species pairs with Oik >0.8 account for only 2.8% of all shrub species pairs, but those pairs with Oik >0.6 take up 87.4%.