Abstract: Changes of photosynthesis and fluorescence parameters of tomato(Lycopersicon. esculentum Mill.) under short time 35℃ sub-high temperature treatment and normal temperature recovery in daytime were studied to investigate the effects of short time sub-high temperature treatment on photosynthetic characteristics of tomato. Plants were treated by 35℃ sub-high temperature for 2 h＋15 min (the even time of measurement，the same as below), 4 h＋15 min, 6 h＋15 min, 8 h＋15 min, then resumed at 25℃ when the 1^st inflorescence effloresced, and plants that under 25℃ all the time considered as control. Results showed that the photosynthesis decreased after plants were treated by 35℃ for more than 2 h. Within the first 2 h that plants were transferred from 35℃ to 25℃ to resume, the photosynthesis continued to decrease. The intrinsic photochemical efficiency(F_v/F_m), quantum yield of PSⅡ(ΦPSⅡ) and photochemical quenching(qP) of plants that were treated by 35℃ for 2 h all decreased, but they could resumed to approach the control level after plants were resumed for 2 hours if they were treated by 35℃ for no more than 6 h. It indicated that plants treated by sub-high temperature only for 2 h, P_n could not recover to the normal level in the same day, and it suggested the decreased P_n under sub-high temperature was mainly caused by no-stomata restriction, but stomata restriction may be the limiting factor that caused P_n decrease during the resumed period.