Abstract: The conventional high power microwave (HPM) radiation measurement system often consists of antennas, attenuators, detectors and other components. There will always be parametric selection dilemma when the conventional system is used in HPM beat-wave radiation measurement, because the system is designed and tested on single frequency while beat-wave signal is composed of many frequency components. Furthermore, the utilization of detectors in beat-wave radiation measurement will lead to new beat-wave frequency components due to their nonlinear feature. It is commonly difficult to measure the output waveform accurately when the signal is superimposed with the new beat-wave frequency components. To solve these problems, a new measurement method based on frequency separation and electric field backstepping is proposed. The application of the proposed method is able to effectively reduce uncertainty of beat-wave radiation measurement to less than 0.3 dB, which satisfies the requirement of accurate HPM beat-wave radiation measurement.