Abstract: The light responses of photosynthesis of Koelreuteria paniculata Laxm. were studied under 4 different soil water conditions, and the light response curves of photosynthesis were fitted and analyzed by rectangular hyperbola model, non-rectangular hyperbola model and a modified model based on rectangular hyperbola model. Then the best model for Koelreuteria paniculata Laxm. was selected. Photosynthetic characteristic were studied under different soil water conditions and different light intensity. The results show that: 1) The light response of photosynthesis were well fitted by the three models, and the modified rectangular hyperbola model could well fit light response of photosynthesis of photo-inhibition. Non-rectangular hyperbola model and modified rectangular hyperbola model is better than rectangular hyperbola model. 2) Koelreuteria paniculata Laxm. had strong adaptability to soil water and light conditions. Higher photosynthetic rate (P_n) and apparent quantum yield (Φ) were observed in the region where the relative soil water contents (R_WC) were from 41.5% to 93.3%. Higher P_n and water use efficiency (W_UE) were observed in the region where the photosynthetic active radiation (P_AR) were from 600 to 2000μmol/(m²·s).