Abstract: 3D printing technology has received more and more attention in the rapid manufacturing of complex shape parts. Mn-Zn ferrite (MZF) was filled into polylactic acid (PLA) as reinforcement, the MZF/PLA composite wire was prepared by ball milling mixing and melt extrusion, and the MZF/PLA composites was prepared by fused deposition modeling (FDM). The micro morphology, mechanical properties and electromagnetic properties of MZF/PLA composites with different composite ratios were characterized by XRD, SEM and vector network analyzer, and the reflection loss of different thickness was calculated to study the effect of MZF content on the microwave absorption properties of the composites. The results show that when the MZF content is 10wt%, the tensile strength of MZF/PLA composite is 17.6% higher than that of pure PLA. With the increase of MZF content, the microwave absorption performance of the composite enhanced. When the content of MZF reaches 50wt% at 12.7 GHz, when the thickness is 7.4 mm, the reflectivity reaches the minimum value of −55.3 dB, and when the thickness is 7.9 mm, the effective microwave absorption band width is 4.5 GHz. Therefore, the 3D printed MZF/PLA composite prepared based on FDM has good microwave absorbing properties and bearing capacity, and it is a very promising microwave absorbing material for 3D printing.