Sweet cherry is the earliest fruit ripen tree in north China and mainly cultivated in Taian, Yantai and Dalian. In recent years, due to the early rise of spring temperature in south China and the rapid development of leisure and sightseeing agriculture, sweet cherry had gradually developed to the south. However, high temperature was more frequent in south China in summer. The influence of temperature on plant are various, which can lead to reactive oxygen species (ROS) in a large number of accumulation in plants and the stability of the biofilm fall and the permeability increases, large molecules such as proteins and nucleic acids, DNA rupture, enzymatic reaction efficiency drops, organelles such as chloroplasts and mitochondria structure was damaged and photosynthetic rate decreased significantly, growth and development, Eventually, the yield and quality of plants were severely reduced. Meanwhile high temperature was closely related to the double pistil rate of sweet cherry. The fruit setting rate of sweet cherry was affected, especially the commercial fruit rate. High temperature became a limiting factor for the southward development of sweet cherry. To investigate the response mechanism of sweet cherry to high temperature stress, the effects of natural high temperature treatment and stress recovery on physiological indexes and ultrastructure of grafted pot seedlings of 1-year sweet cherry were studied in this research. After the seedlings were treated at the average maximum temperature 57.7℃ in consecutive 3 days, the catalase (CAT) and ascorbic peroxidase (APX) activity, superoxide anion (O₂^·-) producing rate and coefficient of the photochemical quenching (qN) increased significantly in sweet cherry leaves. The osmotic regulation substances including soluble protein, soluble sugar and proline content increased significantly. The glutathione reductase (GR) activity, chlorophyll content, PSII maximum photochemical efficiency (Fv/Fm) and the electron transport rate (ETR) were significantly reduced. The activities of superoxide dismutase (SOD) and peroxidase (POD) and the photochemical quenching coefficient (qP) had no significant changes. The ultrastructure of the leaves was also observed. It was found that the stress caused the chloroplast properties change. The part of the grana thylakoid lamellae disappeared, and a large number of giant starch grains and osmiophilic globule appeared. After recovery for 2 days, the activities of SOD, POD, CAT, APX, soluble sugar, soluble protein and total chlorophyll contents decreased significantly, while the activities of GR and proline content increased significantly. The results indicated that the maximum temperature 57.7℃ for 3 days had significant effects on the antioxidant system and photosynthetic characteristics of sweet cherry leaves, and the chloroplast ultrastructure was significantly damaged, causing irreversible damage to the leaves.