Abstract: The electromagnetic environment generated by radiating-wave simulators could simulate the free fields of the high altitude electromagnetic pulse (HEMP) approximately. However, the electromagnetic fields imposed on the devices under the real threat environments were the synthesized fields from the incident waves and the reflected waves. The total fields synthesized by the incident and reflected waves of the free electromagnetic fields on different situations above the lossy earth were calculated. Through comparing the field strengths and waveforms of the total fields with the initial incident waves, the features of the synthesized fields nearby the ground were analyzed. An equivalent calculating method from the simulated environment to the real environment was suggested, and the correction factor of the simulated environment was calculated using this method for the 45 polarized incident wave. Based on the results, we proposed that the devices should be tested for at least three mutually orthogonal orientations and electromagnetic pulse widths should be reduced appropriately for the experiments of radiating-wave simulators.