Abstract: The response of antennas under the irradiation of high power microwave (HPM) plays a key role in the analysis of the response of jamming characteristics and damage effect for back end receiving circuits . In this paper, the response of a planar Archimedean spiral antenna under the irradiation of HPM is investigated,with the help of the time domain finite integration technique together with the Friis transmission equation. The corresponding experiment has been done to validate the results obtained by the theoretical prediction and the EM simulation. The comparisons reveal that a difference of 1dB level for the transmitting power is achieved between the measured data and the theoretical prediction. Moreover, good a greements are also found between the simulated and measured data. It is shown that the analysis method proposed in this paper provides an effective way to investigate the response of antennas to the irradiation of the high power microwave.