Abstract: Crop water availability is crucial to irrigation efficiency in arid regions. It is often required for the interaction between groundwater and soil water in sustainable agriculture. In this study, a systematic investigation was conducted to determine the influence of groundwater table depth (G_WTD) on soil water flow patterns under drip irrigation in mulched cotton fields. Specifically, the depth threshold was identified for hydrologically insignificant capillary contribution from groundwater. Long-term field monitoring (2008-2018) was combined with three-dimensional numerical modeling. Field data were collected from a representative cotton field in Xinjiang, China. Soil moisture dynamics were also observed under natural groundwater fluctuations. The Hydrus-3D model was calibrated and validated to simulate the variably saturated water flow after measurements. Multiple simulation scenarios were executed with controlled groundwater depths from 1.5 to 5.0 m. Soil water velocity fields and system evolution were obtained over a 24-day irrigation cycle. Two hydrological regimes were also observed using decade-long field data. Soil water dynamics followed an ‘evaporation-infiltration pattern’ during 2008-2012. Soil water recharge was attributed to both irrigation and substantial capillary flux from the water table at groundwater depths of 1.4-2.5 m. There was an ‘infiltration-dominated pattern’ at the groundwater levels of 3.0-8.0 m after 2013, when limited irrigation water over short durations failed to reach deep soil layers. Groundwater capillary contribution was minimal. There were three characteristic patterns of soil water flow after simulation at groundwater depth: (1) Saturated-unsaturated zone continuous coupling (G_WTD<3.0 m): there was strong connectivity between the vadose and saturated zones. Four sequential phases evolved: Initial infiltration dominated immediately after irrigation; A zero-flux plane (ZFP) was formed, as soil water potential decreased, thus marking the divergence between upward (evaporation-driven) and downward (gravity-driven) flow; Intense evapotranspiration caused gradual ZFP descent; Finally, a stable stage was dominated by evaporation-capillary rise. The entire soil profile was continuously supplied by groundwater after the ZFP disappeared, and by capillary action. (2) Stratified decoupling (G_WTD≥3.0 m): hydraulic disconnection occurred between soil water and groundwater. Both the irrigation-induced wetting front and the ZFP formation were trapped in the upper soil profile. The infiltrated water percolated downward slowly. But there was no hydraulic interaction with the deep-water table. Soil water circulation was confined to a shallow layer, which was entirely regulated by irrigation and evapotranspiration. Integrated field and simulation showed that the critical threshold was a groundwater depth of 3.0 m controlling transition among the flow patterns, particularly for the dominant sandy loam and sand soils at the study site. The functions were continuously coupled as an integrated hydrological continuum, including “soil water-groundwater-atmospheric water”— in which groundwater acted as a key eco-hydrological buffer, providing for stable internal moisture after capillary rise during peak evapotranspiration periods. As such, an “efficiency-enhancing precision irrigation”strategy was recommended to reduce the irrigation quotas by deducting quantifiable capillary-rise fluxes. Real-time groundwater monitoring was supported to prevent over-irrigation for minimal deep percolation. In contrast, the stratified decoupled system exhibited a “surface-active-deep-static” structure, with the limited hydraulic connectivity to groundwater, leading to reduced resilience and higher dependence on external irrigation. A “precision water-retention irrigation” strategy should be implemented in these areas. Small and frequent irrigation was applied for the moisture in the primary root zone, while reducing non-productive evaporation and deep drainage. Continuous and decoupled flow patterns were identified with the depth threshold. The findings can provide a scientific framework to develop precision irrigation and sustainable groundwater in water-scarce regions, ultimately supporting water use efficiency and sustainability. This work is also limited to water flow only; Future research should advance coupled water-salinity simulations with field validation for the synergistic soil water-salt regulation in the irrigation districts of the arid areas. Important insights can also provide for water resource and irrigation optimization from a hydrology perspective.