Grasslands cover approximately 40% of the global land surface area and play an essential role in the global carbon cycle. In recent years, human activities such as fossil fuel combustion and livestock development have significantly increased nitrogen deposition in the global environment. Grassland management, such as mowing, plays an important role in mediating the effects of nitrogen deposition on grassland plants. In addition, It is important to select suitable models to fit the process of light response and calculate the relevant parameters for studying the photosynthetic characteristics of plants. Based on the field control experiments with the interaction of six nitrogen (NH₄NO₃) gradients and two grassland management modes (mowing and non-mowing) in the Inner Mongolia meadow steppe, the photosynthesis-light response process of Leymus chinensis, the dominant species of the experimental platform, was determined. Four light response models, namely rectangular hyperbola model, non-rectangular hyperbolic model, exponential model and modified rectangular hyperbolic model, were used to fit the light response curves of L. chinensis. The best fitting model of L. chinensis was screened from the fitting effect of parameters and the fitting accuracy of the model, and the effects of nitrogen addition and mowing on light response characteristics of L. chinensis were analyzed. The results showed that the exponential model had the best fitting effect on the apparent quantum efficiency(α), light saturation point (LSP) and maximum net photosynthetic rate (P_nmax), while the non-rectangular hyperbolic model had the highest goodness of fit. In all treatments, L. chinensis did not show obvious photo inhibition, so it had a strongly photosynthetic potential and the ability to adapt to environmental changes. The net photosynthetic rate (P_n), stomatal conductance (G_s), P_nmax, α, and LSP of L. chinensis were increased under proper nitrogen addition and mowing treatment, the utilization rate of light energy of L. chinensis was increased and the utilization range of light intensity was widened. However, the excessive nitrogen application could not further improve the photosynthetic capacity. In conclusion, the exponential model and non-right-angle hyperbolic model were more suitable for fitting the light response curves of L. chinensis under the conditions of nitrogen addition and mowing. Applying 20 g N m^-2 a^-1 and mowing was the best grassland management measure for improving photosynthetic capacity of L. chinensis. In this paper, the effects of different nitrogen concentration and cutting treatment on dominant species of L. chinensis were studied, and the adaptive mechanism of L. chinensis was analyzed from the angle of photosynthesis, to provide scientific basis for future grassland management under the condition of increasing global nitrogen deposition.