The microwave absorption properties of carbonyl iron (CI) and CoFe 2 O 4 ferrite with single-layer and double-layer composite absorbers were investigated based on the electromagnetic transmission line theory and the impedance matching principle in the frequency range from 2GHz to 18GHz. XRD and SEM were used to characterize the structure of the powdered composites. Coaxial method was used to measure the electromagnetic parameters of CI and CoFe 2 O 4 . The reflectances of the matching and absorbing layers of different thicknesses and orders were also calculated. The results show that using CoFe 2 O 4 as matching layer and CI as absorbing layer can greatly expand the coating absorption bandwidth and decrease the reflectance peak. Double-layer absorbers have much better microwave absorption properties than single-layer absorbers. The microwave absorption properties of the double-layer structure are influenced by the coupling interactions between the absorbing and matching layers. The double-layer microwave absorbers with reflection loss less than −10dB over the range from 8.6GHz to 18GHz (the absorption bandwidth is 9.4GHz), which almost covers the X-band (8.2–12.4GHz) and the whole Ku-band (12.4–18GHz) were achieved when the thicknesses of CoFe 2 O 4 and CI were 2.4 and 0.5mm, respectively.