Using double-fluid theory,a microwave attenuation coefficient of hydrogen plasma in Single Wall Carbon Nanotubes (SCNTs),which were grown by iron-catalyzed high-pressure disproportionation (HiPco),is deduced theoretically.In this paper,both the electron collision absorption and ion collision absorption of hydrogen plasma in SCNTs are considered in detail.Under different conditions,microwave attenuation coefficient is calculated theoretically in the frequency range of 0.2-18 GHz.The simulation results show that hydrogen plasma in HiPco SCNTs exhibits strong microwave (around 2.45 GHz) absorption.The numerical results are in good agreement with the experimental data.