Abstract: In the paper, the bandwidths of highelectromagnetic pulses generated by high altitude nuclear explode, lightning, ESD have been investigated. In terms of the energy spectrums of the highEMP and the viewpoint of measurement validity, authors have put forward two new concepts, energy effective bandwidth and dynamic range effective bandwidth, to represent the bandwidth of the highEMP. Both of the effective bandwidths of the highEMP specified in IEC61000－4－4, MIL－STD－464, IEC61312－1 and IEC61000－4－2, have been calculated. In addition, it has been known that the rising time of above highEMP has a little impact on two kind of the effective bandwidth, and it is neglectable within a certain range. At last, the measurement bandwidths of above highEMP are given in according with t