Abstract: Fagus pashanica is an endemic species of Mt. Daba. The forest dominated by F. pashanica mainly distributed in northern Sichuan. We studied the species diversity of F. pashanica forest based on a field sur-vey of 39 quadrats in seven plots in Mt. Daba. The results showed that: (1) A total of 217 vascular plant spe-cies were recorded, belonging to 142 genera and 77 families. Dominant families in the canopy layer included Fagaceae, Ericaceae, Rosaceae and Symplocaceae, while those in the shrub layer were Rosaceae, Caprifoli-aceae, Fagaceae and Aceraceae. In the herbaceous layer, Carex spp. and Pyrola decorata dominated in individual numbers. (2) Logarithm of species abundance showed an inverse “J” shaped distribution pattern in the canopy layer and an approximate normal distribution pattern in the shrub and herbaceous layers. Species richness was highest in the shrub layer and lowest in the canopy layer. Shannon-Wiener index of the shrub layer was higher than those of the canopy and herbaceous layers. Simpson index and evenness index were highest in the canopy layer and lowest in the herbaceous layer. (3) Species diversity was higher on southern and eastern slopes than on northern slope. Regression analysis indicated various relationships between diversity and soil. (4) A significant negative correlation existed between species diversity of the community and the importance values of the dominant species and the main species in the canopy. We conclude that species diversity of the shrub layer is primarily affected by environmental factors, and species diversities of the can-opy and herbaceous layers are affected markedly by both environmental factors and overstory canopy struc-ture.