Abstract: In order to evaluation the effects of drought stress, relative water content, photosynthetic parameter, content of free praline and content of malondiadiadehyde of four forage grasses were analyzed, with the experiment on pot culture with water stress in southwest area. The results indicated that with continuous lasting of drought time, four warm-season forage grasses all displayed the similar physiological characteristics, i.e. decreasing of relative water content, photosynthetic rate, transpiration rate and cond, increasing of content of free praline and malondiadiadehyde. However, the four warm-season forage grasses showed different physiological reaction to the drought stress, and different recovery abilities after re-irrigation. Through comparing the indexes and giving a comprehensive appraisal, the results indicated that the order of drought of forage grasses was Panicum . virgatum L.＞ Paspalum urville S. ＞ Setaria anceps＞ Paspalum dilatatum Poir.