Abstract: The melons variety‘Xizhoumi No.25’and‘Yaolong No.25’were used as test materials,a one-way randomized block test was conducted with four treatments of 30℃,35℃,40℃,45℃,25℃was used as CK,and the temperature and humidity conditions of the facility were simulated in an artificial climate chamber in July,the effects of high temperature stress on the electrical conductivity,malondialdehyde,chlorophyll fluorescence parameters and photosynthetic gas exchange parameters of melon seedlings were studied,in order to provide reference for the stress-resistant cultivation and heatresistant mechanism of melon.The results showed that the conductivity and malondialdehyde were positively correlated with temperature.The electrical conductivity of‘Yaolong No.25’at 35℃,40℃and 45℃increased by 19.03%,36.12%and 54.28%compared with the control.Malondialdehyde was increased by 40.72%,58.46%,81.04% and 132.66% compared with the control.Chlorophyll content,Pn,Gs and Tr of melon were negatively correlated with temperature,while Ci was positively correlated with temperature.Ci increased when Gs decreased.Photosynthetic indices Fo,Fm,Fv/Fo and Fv/Fm were significantly negatively correlated with temperature.Under high temperature stress,the melon variety‘Yaolong No.25’was more suitable for growing in greenhouse.