To clarify the microwave absorbing properties of the hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes (CNTs) in the uniform magnetic field, the microwave attenuation coefficient of the film of magnetized hydrogen plasma in CNTs was deduced based on magneto-ionic theory, Appleton-Hartree Equation and W.K.B approximation. The microwave attenuation coefficient of the film in the range of 0.3~30 GHz under different conditions were calculated. The results indicate that when the external magnetic field strength increases, the frequency bandwidth of maximum ab...