Atmospheric nitrogen deposition increases ecosystem nitrogen availability, and the response of dominant species to different levels of nitrogen input may change grassland ecosystem structure and function. In this study, four nitrogen addition levels were set to analyze the responses of the photosynthetic physiological characteristics of Stipa grandis, a dominant species of temperate grassland in the Inner Mongolia, to different levels of nitrogen addition. The results showed that the nitrogen content of Stipa grandis leaves was lower, chlorophyll content and the ribulose 1, 5-diphosphate carboxylation/oxygenase activity were not high, and the low utilization efficiency of light energy led to excess excitation energy in photosystem II, photosynthetic organ was inhibited, resulting in a relatively low net photosynthetic rate under low nitrogen treatment (0-2 g m^-2 a^-1). Moderate nitrogen addition (5-10 g m^-2 a^-1) improved the nitrogen allocation of leaf carboxylation system and electron transport system, which increased the activity of ribulose 1, 5-diphosphate carboxylation/oxygenase and the electron transfer rate, thereby the net photosynthetic rate of Stipa grandis was increased. Under high nitrogen treatment (25 g m^-2 a^-1), the nitrogen content in Stipa grandis leaves was higher, but the allocation ratio of photosynthetic nitrogen decreased, which reduced the utilization efficiency of photosynthetic nitrogen. Meanwhile, the degree of light inhibition of Stipa grandis was increased, chlorophyll content and the ribulose 1, 5-diphosphate carboxylation/oxygenase activity decreased, which was not conducive to biomass accumulation. These results help to further understand the physiological response mechanism of dominant species in grassland ecosystems under the global change, and provide a certain theoretical basis for the sustainable development of grassland.