Abstract: The attenuation coefficient of electric thruster plasma jet for communication signals was calculated with time-domain finite-difference method. And the attenuation effect on C-band electromagnetic wave propagating through microwave plasma thruster jet was tested at ground using space-wave method. Theoretical calculation and experimental results show that the attenuation coefficient increases almost linearly with the plasma jet frequency, but decreases while the frequency of communication signals increasing. And it has an increasing first then decreasing tendency with the plasma collision frequency increasing. The attenuation coefficient of the C-band communication signal varies from 1.5 dB to 6.0 dB, with the plasma jet density from 0.9×1016 to 1.8×1016. The attenua