Water content is an important indicator to measure the quality of crude oil. In the process of production, storage and transportation of crude oil, the interface of oil-water mixture is constantly changing. Thus, high-precision sensors are used to detect it in the whole process. In this article, an intrusive planar capacitance sensor was designed based on the capacitive edge effect. Its main structure consists of a substrate and a planar electrode array. The 8-electrode array sensor model was established by using finite element software. The electric field distribution of different electrodes was studied, and the detection sensitivity and imaging accuracy of the planar capacitive sensor were analyzed. In addition, the influence of the width, length and adjacent distance of the electrodes on the sensitive field distribution of the sensor was studied. Through the image reconstruction of the dielectric distribution, the designed planar capacitance array sensor can detect the height of the three interfaces, and the size parameters are optimized to improve the imaging accuracy of the sensor. The feasibility and effectiveness of the method of using planar capacitor array to detect oil-water interface have proved by experiments.