Porous carbon skeletons (PCSs) derived from isocyanate-based aromatic polyimide foams (PIFs) by high-temperature pyrolysis are very promising in the fabrication of high-performance polymer composite foams for electromagnetic interference (EMI) shielding due to their efficient conductive networks and facile preparation process. However, severe volumetric shrinkage and low graphitization degree is not conducive to enhancing the shielding efficiency of the PCSs. Herein, ferric acetylacetonate and carbon-nanotube coating have been introduced in isocyanate-based PIFs to greatly suppress the serious shrinkage during pyrolysis and improve the graphitization degree of the final carbon foams through the Fe-catalytic graphitization process, thereby endowing them with better EMI-shielding performance even at lower pyrolysis temperature compared to the control samples. Moreover, compressible polydimethylsiloxane (PDMS) composite foams with the as-prepared carbon foams as prefabricated PCSs have also been fabricated, which could provide not only stable shielding effectiveness (SE) performance even after a thousand compressions, but also multiple functions of Joule heating, thermal insulation and infrared stealth. This study offers a feasible route to prepare high-performance PCSs in a more energy-efficient manner via PIF pyrolysis, which is very promising in the manufacture of multifunctional conductive polymer composite foams.