Abstract: Legume plays an important role in improving soil fertility, protecting soil and water, and providing varied products. However, the degraded grassland made Legume resource destroyed and facing extinction. Here, we emphasized the importance of Legume in grassland ecosystems and summarized advances in studies on photosynthesis and nitrogen fixation, the mechanism of higher photosynthetic rate and the effect of stress habitats on nitrogen-fixing. It was pointed out that it has good future for studying the adaptive mechanism and nitrogen-fixing potential of Legume. Practically, it will be valuable to planting Leguminous shrubs and grasses in man-made forest and pasture to compensate soil for “nitrogen deficiency”.