Abstract: The photosynthetic and leaf traits of four grasses (Zea diploperennis, Medicago sativa, Cichorium intybus, and Pennisetum americanum×Purpureum) were studied in field conditions, together with soil water content and soil bulk density to clarify their physiological adaptability to the Karst rocky desertification environment. There were significant differences of leaf area (LA), dry matter(DW), Chl, specific leaf area (SLA) among these four forage grasses. Zea diploperennis had the greatest LA and DW, while M. sativa had the lowest. SLA was in the sequence C. intybus>M. sativa>Z. diploperennis>P. americanum×Purpureum. M. sativa had the most Chl but there were no obvious differences of Chl between the other three forage grasses, indicating the great differences of the leaf structural traits among these four forage grasses. Z. diploperennis and P. americanum×Purpureum had high P_n, but low T_r and g_s and therefore large WUE and WUEi, but C. intybus and M. sativa were the opposite. This indicated that the intrafamily species Z. diploperennis and P. americanum×Purpureum had similar photosynthetic capacities, while the interfamily species C. intybus and M. sativa had significantly different photosynthetic capacities, even though they shared similar WUE and WUEi. There was no significant difference in water contents in the 0-10 and 10-20 cm soil layers below these four forage grasses, showing that they had little effect on soil water content. However, these different grasses did affect soil bulk density. Correlation analysis showed a significant positive correlation between T_r and water content in the 0-10 cm soil layer for all grasses, and the water content of the 10-20 cm soil layer greatly affected their V_pdl. Comparatively, Z. diploperennis and P. americanum×Purpureum had greater P_n, WUE and WUEi, indicating better adaptability to the Karst environment.