A newly constructed water conveyance tunnel underpasses an existing high-voltage transmission corridor, posing extreme construction risks. Based on risk analysis, this study develops and validates a synergistic reinforcement system for deformation control. Innovatively adopting a controlled-variable approach, multiple scenario groups were designed to systematically quantify the effectiveness of combined measures—including sleeve-pipe grouting for tower foundation reinforcement, micro-pile for isolation protection, and steel arch supports with channel steel sill beams plus multi-angle lock-foot anchors in a two-bench excavation method—through 3D numerical modeling of tower-tunnel interaction and field monitoring. Numerical simulations and field implementation jointly demonstrate that employing micro-piles as isolation barriers, integrated with comprehensive surface and subsurface reinforcement techniques, effectively controls cumulative and differential settlements of transmission towers, maintaining deformations and stress states within safe thresholds. This solution ensures operational safety of high-voltage towers and tunnel construction while significantly enhancing efficiency and cost-effectiveness. Further analysis reveals that the isolation technique outperforms localized sleeve-pipe grouting in mitigating settlements of sensitive structures, with notable advantages in rapid installation and minimal foundation disturbance. The results can provide references for relevant projects.