Abstract: The diurnal changes of photosynthetic rate，Rubisco activity，Rubisco activase（RAC）activity，transpiration rate and intercellular CO2 concentration of cucumber leaves in greenhouse were studied under high temperature and elevated CO2，and the relationship between photosynthetic rate and Rubisco activity，Rubisco activase activity were also analyzed. Main results are as follows：①The photosynthetic rate，Rubisco activity and Rubisco activase activity showed distinct diurnal changes under high temperature and elevated CO2. Compared with the control，high temperature and elevated CO2 led to a remarkable increase in values of the photosynthetic rate，Rubisco activity and Rubisco activase activity. ②Rubisco activase activity had an effect on photosynthetic rate by adjusting Rubisco activity. ③Rubiscoactivase activity and intercellular CO2 concentration were increased by high temperature and elevated CO2，thus photosynthetic rate was improved.

Key words: cucumber, high temperature, elevated CO2, Rubisco activase, photosynthetic rate