Abstract: By using polyethylene glycol (PEG-6000) solution to regulate the water potential of tomato (Lycopersicon esculentum) rhizosphere to simulate water stress, this paper studied the dynamic changes of  net photosynthetic rate, dark respiratory rate and CO₂ compensatory concentration of detached tomato leaves in the process of photosynthetic induction. Under 1000 μmol·m^-2·s^-1 of light induction, the time required to reach the maximum net photosynthetic rate of waterstressed tomato leaves was shortened by 1/3, while the stomatal conductance was increased by 1.5 times, as compared to the non-stress control. Also, the light saturation point (LSP) of water-stressed tomato leaves was lowered by 65% to 85%, and the light compensation point (LCP) was increased by 75% to 100%, suggesting that the effective range of light utilized by tomato leaves was reduced. Furthermore, water stress decreased the maximum photosynthetic capacity of tomato leaves by 40%, but increased the dark respiration rate by about 45%. It was suggested that rapid water stress made the stomata of tomato leaves quickly opened, without initial photosynthetic induction stage. In conclusion, water stress could induce the decrease of plant light-energy use efficiency and potential, being the main reason for the decrease of plant productivity, and stomatal regulation could be the main physiological mechanism of tomato plants to adapt to rapid water stress.