A structure of capacitance sensor used for an automatic car-wiper system is presented. It aims to develop a low-cost sensor with high sensitivity and robustness. Firstly, two kinds of sensing technique based on optical and piezoelectric sensors for an automatic car-wiper system are introduced respectively. Then, three types of capacitance sensors of different shapes are designed. The parameters which affecting the sensor signal strength and measurement sensitivity are discussed. Thirdly, the electric field distributions of the sensors are simulated, and the fringe capacitance of the sensors are measured and analyzed. Finally, the optimum excitation frequency of designed sensor is determined, and the sensor noise is discussed in this paper. The experimental results indicate the validity and importance of the capacitance-based sensing technique which can be used for liquid detection on windshield of vehicles.