The PEA(pulsed electro-acoustic) method is widely used for measuring space charge distribution in insulation materials. However, the measured quantity reflects a voltage curve over time rather than the actual space charge distribution. Therefore, establishing a calibration procedure is crucial to determine the relationship between these two quantities. This calibration procedure aims to convert the measured voltage into the spatial distribution of space charge while correcting for non-idealities such as distortion and attenuation. This paper outlines the main steps of the PEA system calibration and provides a detailed discussion on the selection of the reference signal. Furthermore, recommendations are provided to enhance the accuracy and reliability of the calibration process.