In order to probe into orderliness changes of Glutathione S-Transferase (GST) of chloroplast of Puccinellia tenuiflora seedlings under Na2CO3 stress and its function in resistance to Na2CO3 stress, relative electric conductance, GST activity and the O2-.produce rate of the chloroplast, and the osmotic potential of leaves, and the osmotic potential of culture solution of P. tenuiflora seedlings under different Na2CO3 stress were concerned. The result shows that in the Na2CO3 stress range of 0～0.4%, along with the increase of its intensity under different Na2CO3 stress intensity, GST activity of the chloroplast of seedling leaves of P. tenuiflora is strengthened and GST activity is rapidly weakened with the increase of the intensity of Na2CO3 stress more than 0.4%. The change of GST activity of the chloroplast along with the osmotic potential of culture solution and seedling leaves, relative electric conductance of the seedling leaves as well as the O2-.produce rate have the similar change tendency. There is significant nonlinear relationship among GST activity of chloroplast, osmotic potential of the seedling leaves and Na2CO3 concentration of culture solution, and among GST activity of chloroplast, O2-.produce rate and osmotic potential of seedling leaves, and among GST activity of chloroplast, osmotic potential of culture solution and that of seedling leaves, and among GST activity, the O2-.produce rate of chloroplast and relative electric conductance of the seedling leaves. These indicate that GST of chloroplast plays an important role in the process of seedlings of P. tenuiflora in resistance to the low intensity of Na2CO3 stress.