Abstract: An isolated voltage divider was designed to measure the muzzle voltage for electromagnetic(EM) rail launcher, by which electrical isolation between probe and measured circuit was realized. Parameters affecting the divider frequency response were analyzed, and the range of frequency response was 14 Hz-18 MHz. The designed isolated voltage divider was calibrated by a P6015A voltage probe. The two output signals are in good agreement with each other. The rise time of the pulse is about 1 s, corresponding to the upper frequency of 350 kHz, which indicates that the frequency response of the divider satisfies the requirements of the EM launcher. The resistor divider and the isolated voltage divider were used to measure the muzzle voltage during EM launch. The measured waveforms are consistent with each other. Therefore, the isolated voltage divider meets the measuring requirements of the launcher muzzle voltage.