Abstract: Albizia ocloratissima, Cassia nodosa, Robinia pseudoacacia, and Leucocena leucocephala were considerd as drought resistance plants and grew in dry regions of yunnan. In this experiment, their seedlings were treated with different concentration of polyethylene glycol(PEG). The relative water content(RWC) and plasma membrane permeability of their hypocotyl, the proline accumulation and superoxide dismutase(SOD) activity of their leaves were tested under water stress. The results showed that the RWC decreased and plasma membrane permeability increased with the increase of PEG concentration. There was a negative correlation(r=-0.92, p<0.01) between the RWC and plasma membrane permeability, which indicated that plasma membrane was injured during dehydration. The amount of free proline accumulation increased greatly with water stress. The proline accumulation was related to the RWC of the trees. The proline accumulation level of Albizia ocloratissima which had the highest RWC was the highest. It was suggested that proline plays an important role in the water retention of these species. The SOD activities were intensified when these species were treated with PEG. There was a negative correlation(r=-0.61, p<0.05) between the SOD activity and RWC. Increase of SOD activity was a physiological characteristic of drought resistance plants after water stress. SOD might protect plasma membrane from being injured by O₂^·. So these species were all suggested to be drought resistant. It was helpful for afforestation species selection in drought regions and for the investigation of the physiological features of these drought resistance trees.