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It is significant to reveal the physiological mechanism of water-saving and yield-increasing effects of spring maize (Zea mays L.) under mulched drip irrigation. The objective of this study was to explore the photosynthetic characteristics response of spring maize in a field with drip irrigation under film mulching. Field experiments were carried out from May 2017 to October 2018 for two years at the Heilongjiang Hydraulic Science and Technology Experimental Research Center (45°22′ N, 125°45′ E), located in a typical area of Northeast China, and three treatments were applied: film mulched drip irrigation (MD), non-mulched drip irrigation (ND), and traditional rain-fed practice as a control (CK). The effects of mulched drip irrigation on grain yield and water-use efficiency of maize were analyzed. Based on photosynthetic-light response curves of spring maize leaves at different growth stages from 2017 to 2018, the effects of mulched drip irrigation on photosynthetic capacity, apparent quantum yield, stomatal conductance, specific leaf weight, and 13C carbon isotope discrimination rate of maize were also analyzed. In 2017, the results showed that the yield of MD, ND and CK treatment was 11.0, 10.7 and 9.1 t/hm² respectively, and water-use efficiency was 2.34, 2.06 and 2.11 kg/m³ for MD, ND and CK treatment respectively. In 2018, the results showed that the yield was 12.0, 11.3 and 9.8 t/hm² respectively, and water-use efficiency was 2.70, 2.22 and 2.07 kg/m³ for MD, ND and CK treatment respectively. From 2017 to 2018, photosynthetic capacity first increased and then gradually decreased with the advance of the growth period, and the photosynthetic capacity values ranged from 13.4 to 63.6 μmol/(m²·s). The apparent quantum yield value of different treatments fluctuated between 0.026 and 0.067. The value of stomatal conductance increased first and then decreased with the development of the growth period, and reached the highest value at the jointing stage. The range of stomatal conductance was 0.12-0.50 mol/(m²·s) in 2017 and 0.07-0.47 mol/(m²·s) in 2018, respectively. The specific leaf weight values increased first and then decreased with the advancement of growth stage, and reached the maximum value during the tasseling milk stage. The range of specific leaf weight was 0.040-0.087 kg/m² in 2017 and 0.062-0.084 kg/m² in 2018, respectively. 13C carbon isotope discrimination rate value increased with the growth period. From 2017 to 2018, the MD treatment significantly increased the yield by 20.9%-22.4% compared with the CK as well as significantly increased the water-use efficiency by 13.6%-21.6% compared with the ND, respectively. The MD treatment increased the average photosynthetic capacity value significantly by 12.9%-22.8% (P < 0.05), also increased stomatal conductance by 15.7%-27.2%, increased specific leaf weight by 5%-14%, and decreased the 13C carbon isotope discrimination rate of maize, especially in the early growth stage, compared to CK. It showed that mulched drip irrigation could improve the photosynthetic parameters of maize. Also, the MD treatment significantly affected the linear correlation between leaf nitrogen content and photosynthetic capacity, stomatal conductance and photosynthetic capacity, compared with CK, the slopes of the regression line in the MD and ND treatments were higher, which meant that for a given leaf nitrogen content and stomatal conductance, the MD and ND treatments had a higher photosynthetic capacity values than that of the CK. Also, the results showed that photosynthetic N utilization efficiency and stomatal conductance of leaves was significantly improved by film mulching drip irrigation, which might be the physiological reason for the improvement of photosynthetic capacity, and this might be the key reason for that why yield and water-use efficiency in MD treatment could be significantly increased. Based on the above comprehensive analysis, it was found that the increasing or decreasing of these key photosynthetic parameters under mulched drip irrigation was the key reason for the increase of yield and water-use efficiency of spring maize. This study result provided a theoretical basis for the implementation of film-mulching and drip-irrigation technology in cold spring and water-deficient areas. [ABSTRACT FROM AUTHOR]