Abstract: The carbon nanotubes being straight with a diameters of 20～50nm, internal diameter of 10～30nm and length of 50～1000μm were prepared by the catalytic decomposition of benzene using the floating
transition method at 1100～1200℃. Benzene was used as carbon source and ferrocene as catalyst with thiophene. Three kinds microwave absorbing materials were prepared from carbon nanotube,
carbonyl iron powder, carbon nanotube and carbonyl iron powder mixture and epoxy resin respectively. Microwave absorbing properties of these three kinds materials were investigated at the frequency
range of 2～18GHz. The results show that the absorbing peak of carbon nanotubes and carbonyl iron powders composite microwave absorbing material moves to low frequency, compared with those of
microwave absorbing materials containing only carbon nanotube or carbonyl iron powders. The carbon nanotubes used are as dipoles to absorb microwave. In the microwave absorbing materials containing
an electromagnetic loss substance and dipoles, the dipoles as an electron couples generate an inductive current in the electromagnetic field. The induced current then causes a loss current and energy dissipation.
And the Rayleigh scattering and interface polarization are main microwave absorbing mechanisms in the microwave absorbing materials containing carbon nanotubes.

Key words: carbon nanotubes, carbonyl iron powders, microwave absorbing materials, microwave absorbing properties