A synthetic strategy of coating multiwalled carbon nanotubes (MWCNTs) with cross-linkable octa-acrylate polyhedral oligomeric silsesquioxane (POSS) by combining Diels-Alder cycloadditions with atom transfer radical polymerization in a controlled manner is reported. First, the furfury1-2-bromoisobutyrate is synthesized by an esterification reaction from 2-bromoisobutyryl bromide and furfuryl alcohol. Then, the MWCNT-based initiators of atom transfer radical polymerization (ATRP) are synthesized through a Diels-Alder reaction between MWCNTs and furfury1-2-bromoisobutyrate with controlled grafted content. The MWCNT initiators are used to initiate the ATRP reaction of the octa-acrylate POSS on the MWCNT surface. Finally, a core-shell structure with a MWCNT at the center is obtained, with the thickness of the POSS shell adjusted through different initiators from 5, 10, to 15 nm. The POSS-coated MWCNT is compounded with polyvinylidene fluoride to obtain a kind of composite which has both high dielectric permittivity and low dielectric loss.