Set 11 plots in the southern slope of Qinling Mountains in Shaanxi Province,the characteristics of Patrick richness index,Simpson dominance index,Shannon-Wiener diversity index and Pielou evenness index are studied,in terms of the species comprise,diversity index differences and gradient ordination between diversity indices and environmental factors of Pinus tabuliformis and Quercus aliena var.accuteserrata mixed forest,to reveal the relationships between community diversity characteristics and environmental factors.Results indicated that:(1)11 plots record 112 species vascular plants,belong to 45 families 77 genera.The wide distribution species include Rosaceae,Asteraceae,Liliaceae,Pinaceae,Poaceae and Caprifoliaceae.(2)The dominant positions of P.tabuliformis and Q.aliena var.accuteserrata are significant.The auxiliary species in tree layer are less with average only 4.8 and the biodiversity level is low.The species compositions of shrub layer are rich,average 11.4.The herb layer takes second place,average 9.(3)One-way ANOVA analysis indicates difference of diversity indices from 4 different forest layers all reaches extremely significant level (P<0.01),LSD multiple comparison illustrates the values of diversity indices from community overall are the highest,while diversity level of tree layer is the lowest.(4)CCA method divides the distribution of diversity indices from different layers along 12 environmental indicators (terrain factors and soil nutrients) gradient into 3 sectors,they are Ⅰ (medium concentration of soil phosphorus and organic matters restricted area),Ⅱ(non- environmental factors restricted area) and Ⅲ(high concentration of soil phosphorus restricted area);community overall diversity indices are mainly influenced by shrub layer,meanwhile influenced by tree layer evenness indices,but environmental factors nearly have no restrictive roles on tree layer diversity.(5)The main factors causing diversity difference among different layers of community in study area are soil available phosphorus,total phosphorus and organic matter,while elevation,slope and other terrain factors have no significant effects on community diversity.It may be due to soil nutrients direct influence weakens indirect ecological role of terrain factors.Studies show that keeping moderate soil nutrients and improving tree layer evenness by upbringing is an effective measure for maintaining P.tabuliformis and Q.aliena var.accuteserrata mixed forest biodiversity in the southern slope of Qinling Mountains.