Abstract: The FDTD method and near-to far-field transformation based on Kirchhoff integral were used to calculate the induced open-circuit voltage of cables in free space exposed to HPM and UWB pulse. The influence of the parameters of incident waveform and the relation between the peak value of induced voltage and the length of cable were analyzed. The numerical results indicate that the induced voltage varies with the length of cable and the parameters of incident waveform. Variation of induced voltage peak value is not linear with the length of cable. When the length of cable reaches certain value, it is found that the induced voltage has a maximum peak value. With the electric field intensity of 50 kV·m-1, the peak value of induced voltage can come to several hundred volts even to several ten k