The rapid development of communication technologies raises public health concerns regarding electromagnetic wave pollution, These concerns create an urgent demand for high‑performance electromagnetic interference (EMI) shielding structures. However, traditional manufacturing techniques face limitations in fabricating the complex architectures required for efficient EMI shielding. To address above issues, this study employs three types of multi‑walled carbon nanotubes (MWCNT) as conductive fillers, namely MWCNT, hydroxylated MWCNT (MWCNT‑OH), and carboxylated MWCNT (MWCNT‑COOH). The fillers are melt blended with an acrylonitrile butadiene styrene (ABS) matrix and extruded into composite filaments at a filler loading of 12 wt%. The influence of the functional groups on EMI shielding performance is systematically investigated. The MWCNT/ABS composite exhibits the best performance and achieves a 29.4 dB EMI shielding effectiveness (EMI SE) in the X band. This superior EMI SE stems from the uniform dispersion of the MWCNT in the ABS matrix. This uniform dispersion builds a highly conductive network, increases the effective interfaces with the ABS, and yields a high EMI SE. To further enhance the performance, a lightweight honeycomb structure with a cell size of 3 mm is fabricated via fused deposition modeling (FDM) 3D printing technology. The structure lengthens the electromagnetic wave propagation path and promotes multiple reflections and scattering within the pores. This process enhances absorption loss. The results demonstrate that the honeycomb structure significantly improves the EMI SE and achieves 43.5 dB in the X band. This work presents a facile fabrication strategy to polymer-matrix composite structures for high EMI shielding performance.