Context: Despite the effectiveness of dense planting and regulated deficit irrigation (RDI) in conserving water and stabilizing yields in arid regions, the underlying mechanisms of yield formation, specifically the source-sink relationship are still inadequately researched. Objective: This study seeks to explore the impact of varying planting densities and RDI on maize source-sink characteristics to identify yield-limiting factors. The goal is to finding a suitable maize planting model for water conservation and stable yields in arid regions of northwest China. Methods: A two-year field experiment was conducted during the maize growing seasons of 2020 and 2021, with two planting density (70,000 plants/ha (D1) and 90,000 plants/ha (D2)) and three water treatments (full irrigation (W1), mild water deficit (W2) and moderate water deficit (W3)). Results: Under the same degree of water stress, leaf area duration increased with the increase of planting density. The dry matter accumulation at D2 density increased by 10-20 % and 13-20 % under W1 and W2 treatments, respectively, compared to D1. The source-sink differences were positive for most treatments, indicating that total source supply still had a surplus after fulfilling total sink growth. At D2 density, only the D2W2 treatment had a positive source-sink difference in both years, it had the smallest value. The source-sink ratio of D2W2 treatment was 1.08 and 1.02 in 2020 and 2021, respectively. Compared to D2W1, the yield per unit area of D2W2 was slightly lower (2-3 %), but water use efficiency and irrigation water use efficiency increased by 12-14 % and 13-17 % respectively. Conclusions and implications: Mild water stress (W2) applied at high density (D2) effectively regulated the source-sink balance without altering the limiting effect of insufficient sink capacity on yield. While slightly reducing yield per unit area, the D2W2 treatment significantly improved water use efficiency and irrigation water use efficiency and effectively served as a form of regulated deficit irrigation.