[Objective] In order to provide the theoretical reference for the practice of deficient irrigation in sandy soil, the responses of photosynthesis characteristic and matter accumulation of maize to water deficit at the elongation stage was studied. [Methods] A field experiment was conducted in a newly reclaimed sandy farmland in middle reaches of Heihe River Basin. [Results] Compared with the SW(sufficient water supply), deficient water supply(DW) at the elongation stage significantly decreased the soil moisture in 0-40 cm soil layer of newly reclaimed sandy farmland, CO₂ concentration increased 0.5%, relative humidity decrease 6%, and leaf temperature increase 8%. The net photosynthetic rate in DW was 74% lower than that in SW. The transpiration rate in DW was 79% lower than that in SW. The dry matters in stem, leaf, and root in maize in DW were 63%, 47% and 51% lower than those in SD, and the total dry matter in DW was 53% lower than that in SW. [Conclusion] Crop was more sensitive to the fluctuation of soil moisture in sandy farmland, and slight decrease in soil moisture could cause substantial decrease of photosynthetic capacity, and thus could cause negative influence on matter accumulation and distribution in maize.