Abstract: Abstract: In order to study the effects of planting density and regulated deficit irrigation on transpiration, soil evaporation and yield of maize, two planting densities (conventional low density D1 and high density D2) and different irrigation treatments were used in field experiments for three consecutive years from 2017 to 2019 (2017 and 2018 is the maize for seed). The experiment was conducted at the national field scientific observation and research station on efficient water use of oasis agriculture in Wuwei of Gansu Province (102°51′E, 37°52′N). In 2017, four water treatments were set: local irrigation (W1), full irrigation (W2), mild deficit (2/3 of full irrigation per irrigation) in the whole growth period (W3), and full irrigation at silking stage, mild deficit in the rest growth period (W4). Based on the experiment in 2017, the experimental design was adjusted in 2018 with three water treatments: full irrigation (W2), mild deficit (W5) in vegetative growth stage (end of seedling stage, jointing stage), and medium deficit (1/2 of full irrigation amount per irrigation) in vegetative growth stage (W6). In 2019, there were three water treatments: full irrigation (W2), mild deficit at the vegetative growth stage and end of filling (W7), and medium deficit at the vegetative growth stage and end of filling (W8). In 2017, it was border irrigation under film, drip irrigation under film in 2018 and 2019, local irrigation (W1) was irrigated with fixed irrigation amount, and the rest water treatment was irrigated according to soil moisture content. The effects of different planting densities and irrigation treatments on stem flow, soil evaporation between plants, canopy coverage (CC), yield and yield response factors of maize were studied in the experiment. The results showed that the stem flow rate of maize per plant was significantly affected by planting density and water deficit, increasing planting density and water deficit would reduce the stem flow rate of maize, and rewatering could alleviate the decrease of stem flow rate caused by water deficit. Compared with water deficit, planting density has a more obvious effect on CC, and high density treatment has a larger CC. There was no significant difference in soil evaporation during the whole growth period of each treatment. Increasing planting density in all three years of experiments increased yield while decreasing 100-grain quality (except for the 100-grain quality in 2018). Water deficit in the whole growth period obviously resulted in the decrease of yield, while the water regulation deficit in the partial growth period had no significant effect on the yield. At high planting densities, maize plants are more sensitive to water stress, and the same degree of water deficit can cause more severe yield reduction. Compared with local irrigation methods, full irrigation based on soil water content can save 15.09% of water without significant yield change. Increasing planting density under adequate irrigation (W2) increased maize yield by 15.82%, 34.89% and 22.64% in 2017, 2018 and 2019, respectively, compared to low planting density (local density). Compared to local empirical irrigation practices, a mild water deficit treatment (W7) at the late vegetative growth stage and late filling stage of the crop under high density (D2) could save about 23.14% of water with no significant yield reduction. Therefore, increasing planting density and conducting mild water deficit at late vegetative growth stage and late filling stage of the crop can significantly increase yield and reduce water consumption, and the results provide scientific basis for further water saving and yield increase of maize in Northwest China.