Abstract: The dynamic changes of some growth and photosynthesis characteristics of one year old seedlings of Ailanthus ahissima were tested under various salt stress condition in order to study the specific feature of salt tolerance of this tree species .The result shows that salt stress treatments significantly reduce the height growth of tree seedlings .The fresh leaf weights per unit area appear an increasing trend as the increase of salt contents in treatments.However the total leaf-area per seedling appear a decrease trend.Stoma is the major factor affecting photosynthesis in the initial period of treatment and leaf mesophyll is then becoming another major factor affecting photosynthesis in the late period treatments.