Abstract: In order to solve the impact of drought on crop growth and find the physiological threshold of maize leaf for drought resistance, LI-6400 portable photosynthetic apparatus was used to determine the photosynthetic physiological index of spring maize leaves with different light intensities and CO₂ concentrations under different drought stress. Under the severe drought stress, Pn could reach saturation with low PAR while the value was small. Under the same PAR, Pn presented as: normal irrigation > mild drought stress > moderate drought stress > severe drought stress. As drought stress increased, the Gs decreased significantly, and the amount of Ci was also different. Moderate and mild drought stress were significantly influenced by stoma limitation, while severe drought stress was mainly influenced by non stoma limitation. When PAR increased, Tr decreased with drought stress increasing. As CO₂ concentration increased, Pn decreased when the temperature of spring maize leaves was higher than 35℃, Pn achieved the maximum when the temperature was around 30℃; Gs was the minimum at the temperature of 35℃ while CO₂ concentration increased exponentially; Ci at 30℃ and 35℃ were much smaller than Ci at 20℃ and 25℃. Tr achieved the maximum when the temperature was 30℃. The reaction of light intensity was significantly different in varying degrees of drought stress. As CO₂ concentration increased exponentially, the photosynthesis physiological process was also affected by temperature.