The invention discloses a voltage divider calibrating system and a method for calibrating a voltage divider and relates to the technical field of high voltage measurement. The method includes the following steps: generating exponential waves with the characteristics of the fast leading edge and the long wave tail, calibrating the high-frequency cut-off frequency of the voltage divider by the utilization of the rising edge part of the exponential waves, and calibrating the low-frequency cut-off frequency of the voltage divider by the utilization of the attenuating part of the exponential waves. The system comprises a waveform generating device and a calibrating device, wherein the waveform generating device is used for generating the exponential waves with the characteristics of the fast leading edge and the long wave tail, and the calibrating device is used for calibrating the high-frequency cut-off frequency of the voltage divider by the utilization of the rising edge part of the exponential waves and calibrating the low-frequency cut-off frequency of the voltage divider by the utilization of the attenuating part of the exponential waves. With the system and the method, the exponential waves with the characteristics of the fast leading edge and the long wave tail are generated, the high-frequency cut-off frequency of the voltage divider is calibrated by the utilization of the rising edge part of the exponential waves, the low-frequency cut-off frequency of the voltage divider is calibrated by the utilization of the attenuating part of the exponential waves, and thus simultaneous calibration of high-frequency and low-frequency response characteristics of the voltage divider is achieved.