Abstract: The diurnal changes of net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration in different stage of grafting cucumber leaves in greenhouse were studied under high temperature and elevated CO2 coupling. Main results are as follows：The net photosynthetic rate showed distinct diurnal changes under the high temperature and elevated CO2 coupling.Compared with the control,the net photosynthetic rate increased markedly under high temperature and elevated CO2 coupling. The increasing effect of treatment under high temperature with high CO2 concentration was significandy in the early stage, while the increasing effect of treatment under high temperature with medium CO2 concentration was markedly in the rest stage. The direct reason of photosynthesis increasing maybe was the increase of intercellular CO2 concentration of leaf under high temperature and elevated CO2 coupling.