Abstract: 【Objective】To ascertain the physiological reaction and mechanism of adaption to high temperature stress of functional leaves in rice.【Method】For seven day,a study was conducted to determine the effects of high temperature stress(8:00-17:00,37℃,17:00-8:00,30℃)on the chlorophyll content,photosynthetic characteristics,heat stable protein content and membrane permeability of flag leaves in hybrid rice in controlled environment chamber.【Result】The results showed that chlorophyll content and chlorophyll a/b of flag leaves in rice decreased under high temperature stress,increased after high temperature stress,chlorophyll content of high-temperature tolerant cultivar 996 was greater than that of high-temperature sensitive cultivar 4628.The net photosynthetic rate and stomatal conductance of flag leaves declined and substomatal CO2 concentration and transpiration rate of flag leaves increased under high temperature stress,compared with high-temperature sensitive cultivar 4628,high-temperature tolerant cultivar 996 could keep higher photosynthetic characteristics under high temperature stress;Souble sugar and souble protein and free proline content of flag leaves decreased under high temperature stress,but heat stable protein content increased;The increase scope of malonyldialdehyde(MDA)content and membrane permeability in high-temperature sensitive cultivar 4628 was greater under high temperature stress than in high-temperature tolerant cultivar 996.【Conclusion】Under high temperature stress,higher photosynthetic characteristics and chlorophyll content,souble sugar,souble protein,proline,heat stable protein content and lower membrane permeability and MDA content of flag leaves in rice were the physiological basis of high-temperature tolerant cultivar.