Abstract: Under different water conditions some physiological indexes of Swainsona formosa, such as Malondialdehyde (MDA)，soluble sugar, soluble protein, proline, protective enzymes ( SOD,POD and CAT), were determined by using the conventional method of plant physiology in this paper. The results are as follows:1) with increased drought stress the proline content increased gradually, soluble protein content decreased and the increased, there was a mutual compensation relationship between the two indexes. The tendency of content of soluble sugar increasing initially and then decreasing showed the regulation function of osmotic adjustment material to the drought stress. 2) The activities of defense enzymes changed differently under various water conditions, the CAT activities raised with the drought stress. The SOD activity increased at moderate drought stress and declined at severe drought stress. In contrast to SOD activity, but POD activity changes were opposite to SOD. The cooperative synergistic effect among protective enzymes maintained the integrity of cell membrane of leaves. 3) The MDA content increased with drought stress, which means that damage to.Swainsona formosa due to drought stress can be reduced by increasing soluble content, strengthening activity of protective enzymes and antioxygenic ability.