Abstract: In the pediment plain of Altai District of Xinjiang, the temperate forest dominated by species of Populus, develop along the river-valleys. Eight formations and sixteen association groups are described in some detail by this paper, and their distribution is also briefly discussed. Among the tree species recorded in the river-valleys, seven belong to the genus of Populus(P. laurifolia, P. alba, P. canescens, P. nigra, P. jrtyschensis, P. euphratica and P. pruinosa), the others are Betula pendula, Elaeagnus oxycarpa and a few species of Salix (S.alba, S.triandra etc.). In the area where the vast land is covered by the zonal semi-desert and desert vegetation,the particular environmental conditions of the river-valley are responsible for the presence of these forests, which play significant role on the environment, agriculture and animal husbandry of the area.