Abstract: Salt-stress inhibits the height growth of poplar seedlings significantly, and the rate of height growth decreases with the lasting of salt-stress and increase in salinity from 0. 1 % to 0. 3%. Meanwhile, the accumulation of Cl~- and Na~+ in leaves increases. Free proline accumulation in leaves culminates after 2～ 3 days of salt stress, K~+ accumulation increases rapidly after about 2 weeks of Salt stress, both of which decrease after the culmination with the extension of salt stress. The absorption by poplar seedlings of Cl~- and Na~+ doesn’t take place simultaneously. In later sarge of salt stress the value of Na~+ /Cl~- rises gradually. Under 0. 3% level of salinity, this value may reach 1. 5, and the rise of Na~+/K~+ value results from the increase of Na~+ absorption and the decrease of K~+. External K~+ and Ca~2+ can reduce the inhibition of salt stress to height growth to a certain degree, but the effect of K~+ is not as good as that of Ca~2+.