CNTs@SiC Coaxial Core-shell composite absorber was prepared by chemical vapor deposition (CVD) with monatomic silicon and functionalized multi-walled carbon nanotubes (CNTs). The one-dimensional tubular core-shell structure of CNTs@SiC is conducive to the improvement of dielectric properties and the adjustment of impedance matching performance, and effectively improves the initial oxidation temperature of CNTs. The mass ratio of Si to CNTs is a key parameter affecting electromagnetic properties of the composite. When m (Si): m (CNTs) = 1:1.5, the composite has the best absorbing performance. The effective bandwidth reaches 4.8GHz when the thickness is 1.7mm. When m (Si): m (CNTs) = 1:2, the material has the best absorbing effect in X band, with effective bandwidth up to 3GHz. The CNTs@SiC composite absorber not only has excellent absorbing effect at normal temperature, but also is expected at high temperature due to its unique one-dimensional cored-shell structure.