Abstract: Water and nitrogen are critical factors that constrain the sustainable production of dryland agriculture. With increasingly severe crisis of water and nitrogen resources and environment, exploring and optimizing water-nitrogen managements, and hence achieving coordinated and unified resource conservation, high and stable grain production, and high efficiency are of great significance for agricultural development. Key parameters of APSIM (agricultural production system simulator) are calibrated and validated based on spring maize phenology, yield, and field management data from Tuquan, Inner Mongolia Autonomous Region from 2013 to 2022. Combined with meteorological data from 1981 to 2022 at Tuquan, water-nitrogen management scenarios are designed under different water deficit levels. Optimal water-nitrogen managements for spring maize at Tuquan are proposed based on indicators including spring maize yield, irrigation amount, nitrogen application amount, water productivity, and agronomic efficiency of applied nitrogen. Furthermore, the suitable irrigation and nitrogen application amounts for spring maize under different precipitation year types are analyzed. Results show that normalized root mean squared errors of the simulated and observed days from emergence to flowering, days from emergence to maturity, and yield of spring maize are 1.3%, 1.2% and 2.8%, respectively. APSIM can quantitatively simulate the growth period and yield of spring maize. Based on the principle that yield, water productivity, and agronomic efficiency of applied nitrogen of spring maize do not significantly decrease compared to the maximum values of all scenarios, and irrigation and nitrogen application amounts do not significantly increase compared to the minimum values of all scenarios, four management measures with no significant differences can be selected, namely, starting automatic irrigation when water deficit reaches 40%, 50%, 60% at the depth of 0-100 cm, and when the water deficit reaches 60% at the depth of 0-60 cm. Among them, the optimal auto-irrigation management for spring maize at Tuquan is to apply irrigation when the water deficit reaches 60% at the depth of 0-100 cm. In this scenario, the irrigation amount is 171.0 mm, and the nitrogen application amount is 197.8 kg·hm^-2. When the precipitation during the spring maize growing season is 200-400 mm, the appropriate irrigation amount is 233.0-283.5 mm, and the nitrogen application amount is 176.9-219.3 kg·hm^-2. When the precipitation during the spring maize growing season is 401-600 mm, the appropriate irrigation amount is 110.5-148.4 mm, and the nitrogen application amount is 218.3-241.5 kg·hm^-2, respectively. When the precipitation during the spring maize growing season is 601-800 mm, the suitable irrigation amount is 125.0-155.0 mm, and the nitrogen application amount is 211.8-249.9 kg·hm^-2. This study provides a quantitative reference for utilizing crop mechanism models in real-time monitoring, diagnosis, and precise management of crop water and nitrogen.