Abstract:Cut flower chrysanthemum (Dendranthema grandiflora ‘Jinba’) plants were treated with 40 ℃/35 ℃ or 33 ℃/28 ℃ (day/night) for 11 days and then transferred to 23 ℃/18 ℃ for 5 days to study the changes in their photosynthesis and fluorescence parameters under high temperature stress and normal temperature recovery. The results showed that on the 5th day of 33 ℃/28 ℃ treatment, net photosynthesis (Pn) decreased gradually and stomatal conductance (Gs) decreased evidently; while after recovery for 5 days, both Pn and Gs resumed to 80% of the control. At 40 ℃/35 ℃,Pn and Gs decreased dramatically. The increase of intercellular CO2 concentration (Ci) at the early stage under given high temperatures showed that the photosynthesis inhibition by high temperature stress was resulted from non-stomatal limitations. However, 9 days later, stomatal limitation became the mainly cause of photosynthesis inhibition. The intrinsic photochemical efficiency (Fv/Fm), quantum yield of PSⅡ(ΦPSⅡ), and the efficiency of excitation energy capture by open PSⅡ reaction center（Fv′/Fm′） at 33 ℃/28 ℃ and 40 ℃/35 ℃ all decreased, with antenna heat dissipation increased, indicating that reaction center was protected by decreased light capture and efficiency of electron transfer through PSⅡ. The photochemical quenching (qP) at 33 ℃/28 ℃ descended first and turned to rise then, suggesting that the electron transfer was firstly restrained by the stress. Contrastively, qP rose continuously at 40 ℃/35 ℃, indicating that oxygen-evolving complex (OEC) was the location in chrysanthemum photosynthesis apparatus most sensitive to extreme high tempe rature.