Abstract: The carbon nanotubes were prepared by catalytic decomposition of benzene using floating transition method at 1100~1200℃. Benzene was used as carbon source and ferrocene as catalyst with thiophene. The carbon nanotubes are straight with diameter 20~50 nm, internal diameter 10~30 nm and length 50~1000 μm.The Ni-P and Ni-N alloy coatings on the carbon nanotubes were deposited by electroless deposition technique.The magnetic property of Ni-P and Ni-N alloy coated carbon nanotubes and the microwave absorbing property of their composites at 2~18 GHz were investigated. Compared with the carbon nanotube/epoxy resin composites, the absorbing peak of the Ni-P alloy coated carbon nanotube/epoxy resin composites moves to the higher frequency. The absorbing peaks of the epoxy resin matrix composites containing Ni-P and Ni-N alloy coated carbon nanotubes after heat-treatment move to lower frequency. The coercive forces for the Ni-P alloy coated carbon nanotubes, Ni-P and Ni-N alloy coated carbon nanotubes after heat-treatment are 304.34 Oe, 81.65 Oe, 183.85 Oe respectively. It is found that the microwave absorbing peaks of the three different composites move to the high frequency with the increase of the coercive force. The carbon nanotubes or Ni alloy coated carbon nanotubes are used as dipoles to absorb the microwave.