Abstract: Multiple D-dot voltage probes were designed and calibrated to measure the voltage of a 4 MV induction voltage adder. The frequency response test results indicate that the upper limit of the probe frequency is greater than 270 MHz, which meets the frequency response requirements of the voltage signal to be tested. In calibration, due to the different installation positions of the voltage divider and probe, in order to avoid the mismatch of transmission line impedance causing voltage waveform differences in the fast rising voltage signal at different measurement points, a pulse signal with a front edge of about hundreds of nanoseconds is used for calibration. Due to the low-frequency characteristics of the probe meeting both calibration and actual measurement requirements, the accuracy of calibration can be guaranteed. Considering the direct impact of assembly structure and accuracy on the sensitivity of the probe, the output transmission line probe adopts an online calibration method during the step-by-step installation process of the induction cavity. Due to the influence of electrons and other factors on the voltage probe near the diode, waveform distortion occurs, making it difficult to directly measure the load voltage. The results of multiple experiments on a 4 MV device indicate that the difference between the voltage waveform on the output transmission line and its downstream position is consistent with the voltage waveform calculated using the inductance between the two position, indicating that using the measurement results of the upstream voltage probe of the diode to calculate the diode voltage is effective.