Abstract: Physiological indexes such as water potential,relative water content of twigs,chlorophyll content,free proline and so on,were measured and studied in five water conditions by treating water stress of potted seedlings of four tree species in Maowusu region.And the drought resistance capabilities among tree species were compared.The result showed that with the increase of drought stress,the relative water content,chlorophyll content decreased obviously,the relative permeability of plasma membrane and the content of free proline increased.From normal water condition to serious water stress,the values of indexes such as conductance rate,RWC,free Proline of Pinus sylvestris var.mongolica,Populus alba var.pyramidalisa Bunge,Amorpha fruticosa,Salix cheiophila respectively were: conductance rate: 34.19%～39.25%,15.67%～49.77%,18.91%～56.27% and 17.01%～77.26%;RWC:86.47%～58.19%,87.02%～36.42%,90.08%～46.19% and 90.67%～51.19%;Proline:21.26～234.30,32.25～181.93,32.18～284.59 and 24.76～122.16 μg ·g-1(FW).The change of total cholophyll was not so much,the average changing range of broadleaved trees were 3.27～1.82 mg·g-1 and conifers were 2.25～1.05 mg·g-1.Compared with the values in normal water condition,the average relative water content decreased by 40.56%,the content of cholophyll decreased by 1.33 mg·g-1,the relative permeability of plasma membrane increased by 34.19% and free proline increased by 178.14μg ·g-1(FW).The result of the variation analysis of the values of each measured indexe indicated that the drought resistance capabilities of Pinus sylvestris var.mongolica,Amorpha fruticosa were greater,as a result,they are more suitable for cultivation and utilization in arid area.