Abstract: In order to test the high-altitude electromagnetic pulse (HEMP) immunity for the large equipment under test (EUT), a new moveable and polarizable HEMP radiation simulator is designed based on Marx generator and TEM antenna. In this paper, the effects of antenna polarization direction and terminal load to pulse waveform are studied by experimental method, and the uniform zone of the HEMP radiating wave simulator is determined by actual measurement. The results show that the usable test zone of the HEMP radiating wave simulator is the near field zone, and in the test zone the peak field strength decreases in accordance with 1/d², and the pulse width decreases with the distance increasing away the aperture plane of the antenna. In comparison with the transmission HEMP simulator, the HEMP radiating wave simulator has a larger uniform test zone, which is more appropriate for testing HEMP immunity for large EUT.