Species diversity and its change is one of the main indicators of community succession dynamic process.Our objective was to examine the complex relationships between the species diversity and community succession in the successive serials from Pinus tabuliformis forest to P.tabuliformis-Quercus aliena var.acuteserrata mixed forest then to the subsequent Q.aliena var.acuteserrata forest on the south-facing slopes in Qinling Mountains.Changes of species composition and diversity in each vegetation stratum were studied using the method of substituting spatial difference for time change.The results showed that:(1)312 species of vascular plants belonging to 183 genera and 73 families were recorded in 45 quadrats investigated,among which there were 136 herbs,98 shrubs encompassing woody climbers,and 78 trees.The composition of the three communities was that there were 190 species belonging to 117 genera and 52 families,129 species belonging to 95 genera and 60 families,and 178 species belonging to 109 genera and 50 families in P.tabuliformis forest,P.tabuliformis-Q.aliena var.acuteserrata mixed forest and Q.aliena var.acuteserrata forest,respectively.(2)Species evenness and species diversity in herb layer decreased significantly during community succession (P＜0.05),species richness showed a V-shaped trend;shrub layer species richness,evenness and species diversity did not change conspicuously (P＞0.05);There was a significant hump-shaped pattern in species diversity in tree layer along the succession process,and the species diversity reached a peak in the community of P.tabuliformis-Q.aliena var.acuteserrata mixed forest.The studies above indicated that:changes of species diversity presented a hump-shaped model as a whole in the process of community succession of pine oak forests on the south-facing slopes in Qinling Mountains,which agrees with the intermediate species diversity hypothesis;The species diversity may simply be one of the basis or prerequisites to the community stability.