Abstract: The development of lightweight, broadband microwave absorbing materials to cope with severe electromagnetic pollution is a great challenge. In this paper, graphene (GR)-iron-nickel alloy (FeNi50)-polylactic acid (PLA) composites were prepared by fused deposition modeling (FDM) process, and the physical structure, micromorphology and electromagnetic properties of the composites were characterized by XRD, Raman, SEM and vector network analyzer (VNA). The effects of the GR-FeNi50 mass ratio on the microwave absorption properties of the composites were discussed. The results show that, compared with the composites without GR addition, heterogeneous interfaces triggering polarization loss are formed inside the composites, and abundant folds and pores are generated, which enhance the multiple reflections and scattering of microwaves. The minimum reflection loss reaches −40.5 dB and the effective absorption bandwidth is 4.7 GHz (13.28-18 GHz). The excellent absorption performance is attributed to the good impedance matching and the synergy between interfacial polarisation loss, dipole polarisation loss, conductivity loss and magnetic loss. In addition, the GR-FeNi50-PLA composite has advantages in terms of environmental friendliness, ease of processing and scale production compared to the absorbing materials prepared by wet chemical methods.