Space charge phenomena play an important role in dielectric breakdown, and most studies have focused on space charge accumulation characteristic under DC voltage; however, few studies have focused on space charge under square voltage. Consequently, we improved the traditional pulsed electroacoustic method (PEA) to present a new method for space charge measurement under square wave voltage. Using this method, we can measure the space charge distribution under square waveform of various waveform parameters (polarity, frequency, duty ratio, etc.). From the measurement result, it is found that homo-charge is more likely to accumulate under square wave voltage, and the space charge accumulation under unipolar square wave is much larger than that of bipolar square wave. Furthermore, a high frequency square wave will cause more serious charge accumulation, and an increase in the duty cycle will also result in an increase in the amount of accumulated charge. © 2020, High Voltage Engineering Editorial Department of CEPRI. All right reserved.