Abstract: By a field experiment, the stucture and species diversity were studied for Cupressus chengiana plantation under different stand age, planting density and site conditions in Wenchuan and Lixian, the dry valleys of the Minjiang River. The results indicated that (1) The species was relatively rare in the tree layer, mainly composed of Asteraceae, Leguminosae, Rosaceae and Gramineae under forest, and the species diversity was in a decreasing order as herb layer, shrub layer, tree layer. Ailanthus altissima had great regeneration potential as an associated tree species in tree layer, and Artemisia carvifolia was in the dominant position in herb layer. (2) The growth of C. chengiana was the worst on the middle slope, and the coverage of shrub and herb were extremely low under forest. However, C. chengiana grew fast on the upper slope, the crown density of tree layer was high to 0.9. (3) In terms of forest volume and canopy density of C. chengiana, it was listed in increasing order as the upper slope, the lower slope, the middle slope. For vegetation coverage and biomass, the increasing order was the lower slope, the middle and the upper slope. Therefore, as C. chengiana was chosen for afforestation in the arid valleys of the Minjiang River area, the ecological protection forest was preferred to be on the upper slope, the ecological economic forest was preferred to be on the lower slope, and the proportion of photophilous, drought tolerant and local shrub and herb species should be increased appropriately on the middle slope so as to increase the species diversity of the community.