Aiming at the issue that electrode-edge effects are often neglected in traditional coaxial capacitive sensors, which leads to insufficient monitoring accuracy and a weak sensitivity response, an optimized coplanar capacitive sensor was designed, a three-dimensional model with edge-capacitance correction terms was established, and a capacitance-correction formula for the presence of wear particles was also derived. Numerical simulation was used to investigate the electric-field distribution and the sensor response. Highly symmetric electric fields were observed for the coplanar sensor, while the response in the pipeline center was weak. Four electrode configurations with different edge shapes were designed and evaluated. With edge-enhanced electrodes, high detection accuracy is achieved for both ferrous and ceramic wear particles, with detection limits of 70 μm (iron) and 200 μm (ceramic). For the best configuration (Configuration 4), the sensitivity variation percentage (SVP) is reduced from 0.010 8 to 0.005, corresponding to a 53.4% decrease. Overall monitoring accuracy improved by 4%, and the response intensity in the central region increased by 9%. Sensitivity throughout the flow channel is enhanced, and the average repeatability coefficient is 0.82%. It is concluded that the optimized coplanar capacitive sensor provides strengthened support for wear-particle monitoring in engine lubrication systems.