Abstract: ‘Guimi No.12’‘Beitian No.1’‘Fengmi No.2’ and ‘Xizhoumi No.25’ were taken as materials, which were the main cultivars in South China.The activities of superoxide dismutase（SOD）,peroxidase（POD）,catalase（CAT）,and the content of malondialdehyde（MDA） and chlorophyll in seedling leaves under manual simulation high temperature stress were measured, and the physiological indexes such as fruit setting rate, fruit deformity rate, soluble solid content and edible rate of mature fruit in natural high temperature in greenhouse during adult stage were analyzed, the heat tolerance of four muskmelon cultivars by membership function value method were evaluated, in order to provide a theoretical basis for safe over-summer cultivation and varieties selection of muskmelon in south China.The results showed that the activities of SOD,POD,CAT and the content of MDA were significantly increased（P＜0.01）,and the content of chlorophyll was significantly decreased（P＜0.05） under manual simulation high temperature stress during seedling stage of four muskmelons.The natural high temperature in greenhouse during adult stage of four different muskmelon cultivars had great influence on the fruit setting rate, fruit deformity rate, the fruit soluble solid content and edible rate, through comprehensive evaluation by membership function value method showed, the order of heat tolerance of the four muskmelon cultivars at adult stage was the same as seedling stage.The order of heat tolerance of the four muskmelon cultivars was‘Guimi No.12’＞‘Beitian No.1’＞‘Fengmi No.2’＞‘Xizhoumi No.25’.