Abstract: With five temperature gradient treatments, this paper studied the effects of high temperature stress on the photosynthetic parameters and chlorophyll fluorescence characteristics of four Xinjiang hybrid hazels. When the temperature gradually raised from 25 ℃ to 45 ℃, the net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, water use efficiency and light use efficiency of the hybrid hazels decreased gradually, and the decrement was the largest at 35 ℃-45 ℃. The actual photochemical efficiency of photosystem II, electron transport rate, and photochemical quenching coefficient increased slowly with increasing temperature, but decreased sharply when the temperature was raised to >35 ℃. The water consumption for transpiration and the heat dissipation also increased with increasing temperature. Among the four hybrid hazels, Xinzhen No.3 had higher tolerance against high temperature in photosynthesis, belonging to heat-resistant cultivar.