Abstract: The YSZ based CO₂ sensor having compound of Li₂CO₃-Li and Ba co-doped oxycarbonate as its sensing electrode was designed. And the influence of sensing electrode thickness on its performance was studied by the means of CO₂ response detection and impedance spectroscopy. Due to the large amount of electro-active substances involved in the electrode processes but with limited space for its production and transmission,the potentiometric sensor with thinner sensing electrode probably suffered from EMF fluctuations in some small CO₂ concentration ranges. As the electrode film thickened,total impedance of the sensor increased. Meanwhile,EMF response ratio and △E of the sensor decreased,and its transfer electrons were far from 2. All of these phenomena implied the sensor performance deteriorated with the increase of sensing electrode thickness. In a specific sensor design,the sensing electrode thickness should be reasonable and be considered according to its operation temperature.