Abstract: In a bid to discuss the response mechanism of carbohydrate metabolism in tomato leaves to short-term sub-low night temperature. Dynamic changes of accumulation of each organ dry matter，carbohydrate contents and sucrose metabolizing enzyme activities in tomato（Lycopersicon esculentum Mill.）leaves under short-term sub-low night temperature at 9 ℃ for 3 to 9 days and then recover for 9 days at 15 ℃ were studied. The results showed that short-term sub-low night temperature at 9 ℃ decreased the dry matter content of the each organ，increased fructose content，glucose content，sucrose content and total sugar as well as starch content，inhibited the activities of acid invertase（AI），neutral invertase（NI），sucrose synthase（SS）and sucrose phosphate synthase（SPS）. The net photosynthetic rate，dry matter content of the each organ，starch，fructose，glucose content，and so on were all reversible at 15 ℃ for 9 days after treating 6 days at 9 ℃，but the net photosynthetic rate，starch，fructose content and sucrose synthase（SS）were irreversible for recovery 9 days after treating 9 days. Especially，sucrose content，sucrose synthase（SS）and sucrose phosphate synthase（SPS）could not come back to control for recovery 9 days after treating 6–9 days，and the slower recovery rate was，the longer treatment time was. There were significnatly negative linear correlations between sucrose and starch content and Pn，as well as sucrose content and SPS activity. Reduced photosynthesis under sub-low night temperature could be explained by feedback inhibition of end-productandit and it was suggested that the accumulation of end-product in leaves could be the direct factor in regulating photosynthesis.

Key words: tomato, short-term sub-low temperature, recovery, sucrose-metabolizing