Aiming at the limitations of capacitive sensors for water cut measurement in oil–water two-phase systems, including restricted electric field coverage and uneven spatial response, we proposed a helical uniformly distributed sensing structure with a three-dimensional helical configuration in this work. By extending the effective acting path of electrodes, the proposed structure expands the spatial coverage of the sensing zone and homogenizes the electric field distribution within the detection region, which further improves the consistency of capacitive responses induced by variations in oil—water dielectric properties. A three-dimensional finite element model is established using COMSOL Multiphysics software, and an orthogonal experimental design is adopted to optimize the key structural parameters of the helix. Comparative analyses are carried out between the developed structure, an 8-electrode configuration, and a wall-mounted helical structure. Guided by the optimized simulation results, static experimental tests are implemented on oil–water mixtures with varying water cuts to validate the sensing performance of the proposed structure in capturing dielectric variations of oil–water media. The experimental results demonstrate that the three-dimensional helical uniformly distributed sensing structure achieves higher average sensitivity and wider measurement while maintaining favorable linearity and stable output signals. Great consistency between experimental measurements and simulation predictions is observed in terms of variation trends and relative performance. This work provides an effective structural design strategy for water cut detection in oil–water mixtures and multiphase flow parameter measurement.