Both electrostatic and capacitance sensing techniques have been increasingly attractive for gas solid flow measurement. Although independent flow monitoring can be achieved by either an electrostatic sensor or a capacitance sensor, the fusion of them could provide diversified flow information with simplified sensor structure when used for gas solid flow measurement. In this paper, a novel electrostatic coupled capacitance sensor is proposed for gas solid flow measurement, which could simultaneously act as an electrostatic sensor and a capacitance sensor and thus acquires electrostatic and capacitance information within the same sensing space. Through an in-depth theoretical analysis of the sensor principle based on a pair of concave electrodes, a corresponding interface circuit is designed for signal conversion and extraction. Experiments carried out on a single particle test rig and a belt-pulley rig verify that the electrostatic and capacitance signals can be simultaneously obtained from the proposed sensor through the designed interface circuit. Furthermore, a sensor prototype with a three-electrode configuration is designed to measure the particle velocity, concentration, mass flow rate and charge level on a gravity-fed solids flow rig, demonstrating the potential application of the developed electrostatic coupled capacitance sensor for the gas solid flow measurement.