Abstract: Spring maize is an important food crop in the semi-arid region of northern China. However, owing to the low amount and high interannual and intramonthly variability of precipitation in this region, the yield of spring maize is low and unstable. Selecting a suitable sowing time can help increase the yield and yield stability of spring maize. However, it is difficult to determine the optimal sowing time for spring maize because it changes with the various water supply conditions in this region. To investigate the optimal interval of sowing time and optimal sowing time for spring maize in the semi-arid areas of northern China under different water conditions, this study used the calibrated and validated APSIM-Maize model to explore the optimal sowing time of spring maize under different water supply conditions rainfed conditions, irrigation of 60 mm, irrigation of 120 mm, irrigation of 180 mm, irrigation of 240 mm, and potential condition (irrigation of 308 mm) at a typical site in the semi-arid region. The main results of this study are as follows: 1) by taking the 5% quantile of spring maize yield as the threshold for yield difference, the optimal time interval of sowing time could be set at four days as a reference for the serial-sowing experiment and simulation of spring maize. 2) When spring maize was sown between May 14 and 17, the yield guarantee rates under most water supply conditions were higher than those during the other sowing periods. The optimal sowing time for spring maize was significantly associated with water availability during the growth period. With an increase in irrigation amount, the optimal sowing time for spring maize advanced, and the range of the optimal sowing date was extended (rainfed condition: May 14 to 17; irrigation of 60 mm: May 14 to 25; irrigation of 120 mm: May 14 to 29; irrigation of 180 mm: May 10 to 29; irrigation of 240 mm: May 6 to 29; potential condition: May 6 to June 2). Under rainfed conditions, the mean yields of spring maize in the dry years, normal years, and wet years were 0.9, 2.3, and 5.5 t∙hm⁻², respectively. The spring maize yield within the optimal sowing window under rainfed condition, and 60 mm, 120 mm, 180 mm, and 240 mm of irrigation and potential condition were 4.0, 5.7, 6.8, 8.6, 10.1, and 10.4 t∙hm⁻², respectively. 3) The meteorological determining factor of spring maize yield under the potential condition was the solar radiation during growth period. Under 240 mm and 180 mm of irrigation, the meteorological determining factors of spring maize yields were solar radiation and precipitation during the vegetative growth period of spring maize. The growth period precipitation was the meteorological determining factor of spring maize yield under rainfed conditions and irrigation of 120 and 60 mm. Our results revealed the optimal sowing date and its change with the water supply conditions. The results of this study provide a scientific reference for sowing spring maize at a suitable time by considering the water available in the semi-arid region of northern China.