Abstract: This paper proposes a method of generating a square wave excitation signal through an analog circuit, using an analog switch to select the detection channel. In addition, high precision and low temperature drift resistors have been added for calibration. The calibration calculation and impedance detection are performed every 5 minutes. This system greatly reduces the errors caused by analog circuit and external factors and improves the accuracy of measurement. It can be used in the multi-lead EEG acquisition system and has good application value.