Plant species diversity is an index reflecting the complexity and stability of forest community function.Altitude is a prominent factor affecting plant species diversity.In order to investigate the influences of different altitudes on the characteristics of species composition and diversity of Cunninghamia lanceolata plantation in Jiangyou district,Sichuan Province,we conducted a field investigation.Four sample plots were selected in high and low altitude,respectively.The species richness index(D),Shannon-wienner index(H),Simpson index (H′) and Pielou index(J_sw) were adopted to evaluate the level of species diversity in C.lanceolata plantation.The results indicated that:(1)A total of 205 species belonging to 66 families and 177 genera were found in this study area.7 trees,54 shrubs,47 herbs and 10 trees,60 shrubs,41 herbs were included in low and high altitude,respectively.(2)In terms of species composition,the high and low altitude contained similar woody plants.(3)The species diversity at both low altitude and high altitude in different layers of these communities was in a decreasing order of herb layer>shrub layer>tree layer.Species diversity index showed regularity in certain range along with the increasing of altitude.The species D,H and J_sw were demonstrated as high altitude>low altitude;while the H′ was converse.An increasing trend in species diversity and evenness of species distribution at high altitude was found,which may be related to the slight human disturbance and variable environmental factors.