Abstract: The present study aimed to characterize the photosynthesis of leguminous grasses in different months. Three kinds of leguminous grasses, including Melilotoides ruthenica, Lespedeza davurica, Medicago sativa, were selected as experimental materials. The environmental temperature（Ta） and the photosynthetically active radiation（PAR）, stomatal conductance（Gs）,transpiration rate（Tr）, intercellular CO2 concentration（Ci） and net photosynthetic rate（Pn） of leaves of the three kinds of leguminous grasses were determined for three successive months, and the instantaneous water use efficiency（WUE） and light use efficiency（LUE） were calculated based on the related parameters mentioned above. The results showed that Melilotoides ruthenica was a low-photosynthesis, low-transpiration, and low-LUE typed plant, indicating that it was suitable to be planted in arid and low temperature regions; for Lespedeza davurica leaves, Pn was negatively correlated with Ci, LUE was very significantly positively correlated with Gs and significantly negatively correlated with WUE, and WUE was significantly positively correlated with Gs, indicating that they had stable ability in absorbing CO2; Medicago sativa was a high-photosynthesis, high-transpiration,and high-WUE typed plant whose leaves Pn was significantly positively correlated with Tr, indicating that it had significant CO2 fixation effect and was an ideal plant for alleviating greenhouse effect.