Abstract: Electromagnetic absorbing materials with light weight, high strength, wide absorption band, thin thickness and thermal stability are the core requirements for microwave absorption applications. In this paper, Fe₃O₄-MWCNTs/PLA composite wires were prepared by ball milling mixing and melt extrusion using polylactic acid (PLA) as matrix, Fe₃O₄ and multi-walled carbon nanotubes (MWCNTs) as fillers, and Fe₃O₄-MWCNTs/PLA composites were prepared by melt deposition molding (FDM). The phase structure, microstructure and electromagnetic properties of the composites were characterized by XRD, SEM and vector network analyzer, respectively. The composite absorbing material of Fe₃O₄-MWCNTs/PLA has light weight, good stability, and adjustable dielectric properties, which exhibits excellent broadband absorption ability due to its good impedance matching and electromagnetic wave attenuation ability. The experimental results show that when the Fe₃O₄ content reaches 25wt% and the thickness is 1.4 mm, the reflection loss reaches −48.5 dB and the effective absorption bandwidth reaches 6.78 GHz (10.38-17.16 GHz), showing excellent microwave absorption performance.