In the location of thunderstorm clouds, the measurement of the relative dielectric constant of the ground surface is very important. In order to solve the problem of continuous monitoring of surface media, this paper analyzes the measurement principle of the same surface plate capacitance sensor, builds the design model of the same surface plate capacitance sensor, and completes the sensor plate design based on the actual surface monitoring application scenarios; The Debye relaxation relation of dielectrics is introduced to find the best driving signal frequency suitable for surface dielectric measurement; Design and build the signal measurement circuit, introduce temperature and humidity compensation, and improve the measurement accuracy; The least square method is used to linearly fit the best data matching function. The experimental results show that the measurement error of the system can be controlled within 5%, which can effectively monitor the relative permittivity of the ground in real time.