Abstract:The 19 tested cultivars were selected from the grape germplasm resources pool of Turpan Research Institute of Xinjiang Academy of Agricultural Sciences. We determined 12 physiological indexes, such as gas exchange parameters, chlorophyll content, antioxidant enzyme activities and proline content, in grape leaves under field condition during the middle period of local natural high temperature (July, Daily maximum air temperature>35 ℃). We furtherly evaluated the heat tolerance of different varieties by fuzzy membership function analysis and optimal segmentation clustering of ordered samples. Investigated physiological response to high temperature and evaluated heat tolerance of different grape cultivars, which would provide a theoretical basis for taking appropriate cultivation managements to reduce the impact of high temperature and breeding of high temperature tolerance grape varieties. The results showed that: (1) in the natural high temperature condition, the 19 tested grape varieties responded differently to high temperature. ‘Red Globe’, ‘Fujiminori’ , ‘Beta’ and ‘Hetianhuang’ had strong heat tolerance, while ‘Thompson Seedless’, ‘Hongqi Tezaomeigui’ , ‘Shuijing Wuhe’, ‘Victoria’ , ‘Yatomi Rosa’ and ‘Crimson Seedless’ had weak heat tolerance. (2) Among the 12 physiological indexes, malondialdehyde content and antioxidant enzyme activities were mostly different in various grape varieties. The strong heat tolerance grape cultivar ‘Red Globe’ and ‘Fujiminori’ had relatively lower malondialdehyde content, ‘Beta’ and ‘Hetianhuang’ had relatively higher malondialdehyde content, but they hadhigher activities of antioxidant enzymes. (3) The result of fuzzy membership function analysis showed that the cumulative membership value(AR) of each physiological index is consistent with the apparent heat resistance performance, which AR can be a potential index to evaluate the heat tolerance of grape varieties. Further cluster analysis classified the tested cultivars as strong, medium and weak. ‘Red Globe’, ‘Fujiminori’, Beta and ‘Hetianhuang’ had stronger heat tolerance.