Abstract: In order to find out the optimum light response model of photosynthesis, compare the advantages and disadvantages of different models, understand physiological ecology characteristics of photosynthesis of Paspalum notatum and reasonably use water resource to conduct vegetation recovery, three light response models were used to simulate light response. Light response process of photosynthesis was studied by Li-6400 photosynthesis system under different soil water stresses in rainy season in Yuanmou dry-hot valley, light response curve was simulated by rectangular hyperbola model, non-rectangular hyperbola model and modified rectangular hyperbola model, respectively. The difference of the three models was analyzed by determination coefficient (R2), simulated initial quantum efficiency (α), the maximum net photosynthetic rate (Pnmax), light saturation point (LSP), light compensation point (LCP) and dark respiration rate (Rd). The results showed that (1) Pnmax, LCP and Rd of Heteropogon contortus decreased with the increase of water stress, light suppression phenomenon happened under strong light situation, photosynthetic (Pn) increased and then decreased with the increase of photosynthetically active radiation (PAR); (2) according to R2, the simulation results followed the order of modified rectangular hyperbola model ＞ non-rectangular hyperbola model ＞ rectangular hyperbola model; (3) the four parameters of Pnmax, LSP, LCP and Rd were close to the measured values in rectangular hyperbola model, while most of the parameters of other models had obvious differences from the measured values except individual parameters. Modified rectangular hyperbola model could get saturated light intensity and Pnmax directly, and well fit the light response process and characteristic parameters, the simulated values could meet the actual physiology condition and the measured values, thus this model could simulate the light response characteristics of photosynthesis of Paspalum notatum under water stress.