A novel approach is developed to study the electromagnetic wave absorption properties based on chemical molecular structure in this work. The MWNT-g-ABPBO composite with core-shell structure, initiated by macromolecule MWNT-benzocyclobutene(ethyl 2-bromoisobutyrate) (MWNT-BCB(EBIB)) via ATRP method, exhibits outstanding electromagnetic wave absorption properties in the Ku band. Traditionally, the electromagnetic wave absorption occurs around the wavelength of 3 cm (at 8 GHz), while the studies on materials with absorption properties at the wavelength slightly under 1.5 cm (at 20 GHz), namely part of the Ku band, are limited. The absorption peak of MWNT-g-ABPBO composite, with the thickness of 2.8 mm, can reach -36 dB at 17.4 GHz, because of the excellent impedance matching between the initiator and monomers bearing highly conjunction chemical structure introduced by ATRP. Meanwhile, the maximum reflection loss (RL) was -47 dB at the frequency of 15.5 GHz and the effective absorption bandwidth (<-10 dB) is from 13 to 18 GHz.