Hot Pepper is a common vegetable grown in greenhouse, but it usually encounters high temperature stress.Changes in photosynthesis and quality of hot pepper (Capsicum annuum L.)seedlings were investigated after plants were treated to different irrigation amounts under the elevated temperature stress.Seedlings were divided to three groups and irrigated by 80% evapotranspiration (ET), 100% ET and 120% ET separately.These groups were identified as T1, T2, and T3 respectively.Results showed that both the net photosynthetic rate (Pn) and the intrinsic photochemical efficiency (Fv/Fm) of seedlings in T3 were the highest among treatments.And significant decrease in Pn and Fv/Fm were observed in T1 compared to T3.Taking stomatal conductance (Gs), intercellular CO2 concentrations (Ci), the rate of transpiration (Tr), and the limitation of stomatal conductance (Ls) into account, the decrease in Pn of T1 and T2 was mainly caused by stomatal restriction.The seedlings healthy index and growth function showed a similar trend as follows: T3 > T2 > T1.So it was concluded that 120% ET supplementary irrigation was suited to the growth of pepper seedlings under the elevated temperature stress in greenhouse.The modest increase in irrigation amount may be able to alleviate the negative effects of elevated temperature on plants.