In order to realize array measurement of water holdup on oil well section, a capacitance-based sensor with planar inter-digital structure is proposed, an integrated detecting module is designed, which converts the measured capacitance value to periodic signal with corresponding frequency, a circuit which extracts signal from current change of power supply is developed. The experimental result shows the above solution has advantages to minimize size sensor, less connections between sensor and circuit boards, strong anti-interference performance and high definition when water holdup is not above 50%, thereby, it has important reference value for developing array capacitance-based log tool for water holdup measurement.