Use maize Jidan 261 and Jingdan 28 as materials. Research the effects of water stress on chlorophyll fluO₂ rescence parameters of maize leaf. The result sho wed that the light2saturated net photosynthetic rate, light compensation point and light saturation point and values of intrinsic quantumefficiency for CO₂uptake were decreased on water stress. The basis fluorescence of the maize leaveswas significantly increased. The max fluorescence, the variable fluorescence and photochemical efficiency were significantly decreased. With the increased of light, The photochemical quenching coeffi2 cient and actual photochemical efficiency were significantly decreased. But the non2photochemical quenching coefficient and apparent electron transport rate were increased slowly. Result showed that the photosynthesis competence ofmaize leaf was lo wer under stress.The inverse proportion of PS ò was unfolded slowly.The capability of electron transport of photO₂ synthesis was decreased, and PS ò latency active was restrained. The superabundance light was dissipation by other aP₂ proach such as non2photochemical quenching mode.To protected photosynthetic structures from injure.