People need to measure rainfall accurately in many cases, and hence improving the accuracy and real-time performance of rainfall sensors is a current problem. A new type of rainfall sensor based on a proximity capacitance array is proposed. The sensor can be used to detect the rainfall coverage of an insulator surface accurately and efficiently. According to the different characteristics of dielectric constants of different materials, the water film thickness on the surface of the insulator is measured by using the principle of proximity capacitance, and a comprehensive evaluation index of sensor performance is proposed. The finite element method is utilized to compare the characteristics of capacitance sensors using three types of electrode to improve sensor penetrability and achieve high water film detection sensitivity. An electrode array is designed according to optimal results, and multielectrode measurement data are aggregated to determine the amount of rainfall. Moreover, an experimental sensor platform is constructed to verify the proposed rain sensor based on a proximity capacitance array. The designed rainfall sensor possesses good accuracy, and the measurement error is about ±2.3%. The proposed rainfall sensor allows for accurate real-time measurements of rainfall on insulator surfaces with a certain thickness.