Shanxi Province is located in the east of China's Loess Plateau. Traditional agriculture is restricted by the poor environmental conditions, water shortages and low soil fertility. The only way to develop agriculture is by adjusting the methods used to the local conditions and the development of animal husbandry. The shortage of browse and forage resources requires us to find appropriate grass species for the local conditions. Panicum virgatum L. and Galega orientalis Lam. cv. xinyin No.1 are two high yield and high quality grasses, so we introduced and cultivated them in the city of Taiyuan, Shanxi Province, China. By observing their phenophases, production, suitability, nutritional content, and so on, we found these two forage species can complete their reproductive cycle in the local climate and environmental conditions and they have many strong points such as better suitability, higher production and better quality than other species. We needed to do further study on them before introducing them as new species for Shanxi Province. We studied the photosynthetic characteristics of these two grasses in detail to determine if they could be introduced and cultivated in the Province. We analyzed the relationships between the diurnal changes of photosynthetic characteristics and environmental factors at different stages of growth. We also studied the characteristics of how leaf gas exchange indicators responded to changes in the natural environment, including especially light intensity. The findings confirm the adaptability of these two grasses and provide theoretical reference for their introduction and cultivation as well as a scientific basis for the establishment of sustainable grassland agriculture in this region.We selected different stages of growth in these two species to measure their photosynthetic and ecophysiological characteristics using a Portable LI-6400 Photosynthesis System (LI-COR, Inc., Lincoln, NE, USA) on 25 May, 6 July and 25 August 2010. The results show there were significant differences in the diurnal variations and light-response curves. (1) Xinyin No.1: The diurnal change of the net photosynthetic rate (P_n) had a bimodal pattern and had a clear midday depression. The daily averages of P_n, light use efficiency (LUE) and water use efficiency (WUE) during the branching stage were higher than in the podding stage. However, the daily averages of leaf temperature (T_l), transpiration rate (T_r), stomatal conductance (G_s) and intercellular CO₂ concentration (C_i) in the podding stage were higher than in the branching stage. (2) Panicum virgatum: The diurnal change of P_n had a unimodal pattern. The daily averages of P_n and T_r in the jointing stage were higher than in the heading stage, and were also lowest during the flowering stage. The daily averages of WUE and C_i in the flowering stage were higher than in the jointing stage, which were the lowest during the heading stage. The daily averages of LUE and T_l in the heading stage were higher than in the jointing stage, and were the lowest during the flowering stage. (3) P_n was significantly positively correlated with T_r, G_s, stomatal limiting value (L_s), and photosynthetically active radiation (PAR), but significantly negatively correlated with C_i. T_r was significantly positively correlated with G_s, vapor pressure deficit (V_pdl), air temperature (T_a), T_l and PAR, but was also significantly negatively correlated with air CO₂ concentration (C_a). T_l and G_swere significantly positively correlated with PAR. (4) By drawing the light response curves and by taking the relative physiological indexes into account, we could draw the conclusion P. virgatum is a heliophilic plant and Xinyin No.1 is a shade tolerant plant based on relevant evaluation criteria. Also, P. virgatum has greater adaptability to diverse environments than Xinyin No.1.