Context or problem: The maize-soybean intercropping system, as a typical resource-intensive agricultural model, exhibits constrained productivity due to resource competition caused by interspecific root niche overlap. Objective or research question: We proposes a regulated deficit irrigation (RDI) strategy that accounts for the spatiotemporal water demands of intercropped crops, aiming to improve interspecific water complementarity and decrease rhizosphere competition. Methods: Four irrigation treatments were implemented: MSW1 (conventional irrigation, full irrigation for both crops), MSW2 (full maize with RDI soybean), MSW3 (RDI maize with full soybean), and MSW4 (RDI for both crops). Results: Two-year field trials demonstrated that compared to MSW1 treatment, the MSW2 treatment stimulated maize deep root proliferation (+ 11-65 % in root tissue density), enabling maize to better utilize subsoil water originally accessed by soybean (+ 182-284 %). This strategy reduced irrigation volume by 9.4 %-17 % without compromising yield, while achieving a 29 % reduction in evapotranspiration and an 12 % improvement in water equivalence ratio (WER). Water use efficiency (WUE) and economic water use efficiency (EWUE) increased by 28-29 %, respectively. Grain yield under MSW2 surpassed other deficit treatments (MSW3 and MSW4) by 46 %- 49 %, with 30 %-34 % of this yield advantage attributed to root spatial niche superposition effects and 70 %- 167 % enhancement in interspecific hydraulic compensation effects. Conclusions: Our results demonstrated that RDI can serve as an effective management tool to intentionally reshape root system interactions in maize-soybean intercropping, shifting belowground relationships from strong competition toward more complementary water use. Prioritizing full irrigation for maize while applying moderate and growth stage-specific deficits to soybean emerges can conserve water and enhances both WUE and economic returns without compromising yield. Implications or significance: The proposed "full maize with RDI soybean" strategy can be readily implemented in existing drip irrigated intercropping systems and provides a concrete pathway for sustainable intensification of maize-soybean production in water limited agroecosystems. Future work combining this framework with high throughput root and canopy phenotyping, sensor based smart drip irrigation control and multi-site evaluations will be important to optimize and scale this approach under diverse climatic and management conditions.