Water deficit is one of the major rate-limiting factors for plants growing in arid and semiarid region and directly reduce the plant's photosynthetic rate. Tomato (Lycopersicon esculentum Mill.) is one of the most valuable commercial vegetables all over the world and widely cultivated in China whether in open field or in greenhouse. Light-responsive photosynthetic model provides the reference to evaluate and simulate the plant photosynthesis production and the production capacity of the ecological system. The maximum net photosynthetic rate(P_max) and apparent quantum yield(α) derived from light response curve are the vital parameters of light-responsive photosynthetic model, which are the critical physiology-ecology parameters of plant photosynthesis characteristics and vary with the plants species, varieties, growth condition and their metabolic status etc.. The leaf age directly affects the efficiency of plants photosynthesis and the values of light-responsive photosynthetic parameters. Water deficit could accelerate leaf senescence and shorten the leaf lifespan. Even the photosynthetic performance of leaves under different water conditions shows the obvious difference at the same leaf age. Up to now there are a few pieces of works reported on light-responsive photosynthetic characteristic of photosynthesis in different age of tomato leaves under multiple supplementary irrigation level. The objective of this study is to profile light-responsive photosynthetic characteristics in tomato with different leaf age of leaves under different levels of supplementary irrigation amount, which will provide the light-responsive photosynthetic parameters for photosynthetic model under different water condition and leaf age. In this study, tomato plants potted in greenhouse as material, the gas exchange and light-responsive photosynthetic characteristics parameters of tomato leaves with the change of leaf age under 4 levels of supplemental irrigation amount (50%ET, 75%ET, 100%ET, and 125%ET) were investigated. The results showed that net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) all gradually reduced, but water use efficiency (WUE) ascended firstly and then descended with the increase of tomato leaf age; When leaf age were 18 d and 29 d, both P_max increased and then decreased with the increase of supplementary irrigation amount, peaking at 75%ET and 100%ET, respectively. When leaves age were 38 d and 47 d, with the rising of supplementary irrigation amount, both P_max ascended, peaking at 125%ET treatment. As for α, it rose with leaf aging, reaching a peak at the leaf age of 38 d. And for light saturation point (LSP), it decreased with leaf aging. The light-responsive photosynthetic parameters of different leaf age of tomato leaves under different supplementary irrigation amount were as follows. When leaf age was 18 d, P_max was 20.64-26.73 μmol·m^-2·s^-1,α was 0.0518-0.0556; when leaf age was 29 d, P_max was 11.00-24.24 μmol·m^-2·s^-1; α was 0.0522-0.0594; when leaf age was 38 d, P_max was 11.77-18.18 μmol·m^-2·s^-1,α was 0.0619-0.0693; when leaf age was 47 d, P_max was 9.09-18.17 μmol·m^-2·s^-1,α was 0.0538-0.0606. In conclusion, with leaf aging, increasing supplementary irrigation amount could delay the fall of photosynthetic capacity of tomato leaves. Stomatal limiting factor was the main factor of influencing photosynthesis of tomato leaves; Stomatal limiting and non-stomatal limiting factors were the causes of photosynthetic rate varying of tomato leaves according to the leaf age.