Abstract: In order to broaden the bandwidth of high power microwave radiation antenna, an X-band high power circularly polarized reflectarray antenna constructed by mechanically rotational helical elements is proposed and investigated. The array antenna is fed by an X-band left-handed circularly polarization circular horn. The variable rotation of helical element enables full 360° phase adjustment with low reflection loss. The rectangular reflectarray antenna of 225-element is put forward and simulated. Full-wave simulation result shows that at 9.3 GHz, the antenna gain is 28 dB, the antenna axial ratio is 0.53 dB and the aperture efficiency is 52.6%. In the range of 8.5 to 10.9 GHz, the gain is over 26.8 dB, the axial ratio is below 1.14 dB, and both the 1-dB gain bandwidth and the 40% aperture efficiency bandwidth are over 21%. The power handling capacity of the reflectarray antenna is found to be 207 MW in vacuum.