A deep-rooted tree ecosystem and its root water dynamics and uptake are challenging to understand. This study investigated the fine-root-growth patterns and soil water use of apple trees down to 25 m in the long-term waterlimited Chinese Loess Plateau (CLP). The soil water and root characteristics were sampled in 2016 and 2020 across five apple orchards planted in 1994, 1998, 2001, 2005, and 2008. We found that deep soil water storage loss (5-25 m) was significantly depleted, with gradual, sharp, and steadily increasing trends in young, mature, and old orchards, respectively. Characterization of the root systems revealed that while the maximum rooting depth (MRD) increased with orchard age, the rate of fine roots deepening declined after 19-year-old. Crucially, the evaluation of precipitation variability revealed a non-linear relationship between MRD and orchard age, driven by successive dry and wet cycles. A polynomial relationship between soil water storage (SWS) and MRD was observed in response to sequential weather extremes. The deep rooting of perennial apple trees represents a significant adaptation to dynamic deep soil water availability, enabling trees to mitigate surface water deficits by accessing deeper soil water reserves over the long term. Our findings underscore the necessity for adaptive water management strategies in CLP apple orchards to maintain productivity and ensure the long-term viability of this crucial agricultural industry.