Abstract: In this experiment，Jinyou 37 was selected as the material to study the relationship between photosynthesis and starch content of grafted cucumber in greenhouse at elevated CO2 conditions. The results showed that：① High temperature treatment inhibited the net photosynthesis rate of cucumber leaves and reached at the peak level after treatment of 22 days，content of starch and carbohydrate was the lowest of the treatments. ② The photosynthesis could be promoted with elevated CO2. It reached at the peak level after 29 days of treatment with elevated CO2 at ambient temperature，while treatment with elevated CO2 at high temperature extent to 36 days. ③ Content of carbohydrate presented the opposite changes with starch content. Starch content was higher than control after treatment of 36 days withelevated CO2 at high temperature condition；Content of starch with elevated CO2 at ambient temperature started to increase after treatment of 22 days，of which was earlier than the other treatments in terms of the starting time of the starch accumulation，but its net photosynthesis was lower than control after treatment of 36 days，starch content t had significant negative correlation relationship with the net photosynthetic rate，which turned out that the accumulation of starch made a feedback to photosynthesis in cucumber leaves.

Key words: cucumber, high temperature, elevated CO2, starch, photosynthesis