Metallurgical defects significantly affect the performance of materials fabricated by selective laser melting (SLM), becoming a bottleneck problem in the application of laser 3D printing technology. To investigate the effect of metallurgical defects on the magnetic properties of SLM NiFeMo permalloy. An in-depth characterization of the microstructure and phase composition of SLM-fabricated NiFeMo permalloy samples were carried out. Soft magnetic DC BH hysteresis loop tester was used to assess the magnetic properties. Defect voxel data of as-built samples were obtained using X-ray microcomputed tomography (XCT). The results show that the micro-defects of SLM NiFeMo alloy are mainly composed of lack of fusion, pores, etc., and the phase composition of NiFeMo is mainly γ- (Ni, Fe) solid solution. With the increase of laser volume energy density, the Bs and μm of the material increase, while the Hc and Pu decreases. The equivalent diameter of the defects shows a positive correlation with the coercivity (Hc) and a negative correlation with the saturation magnetic induction (Bs) of NiFeMo permalloy. •The microstructural features, the evolution of defect size and morphology were analyzed and described in detail.•Defect data information in SLM-fabricated permalloy was extracted and quantified using XCT.•Permalloy samples with relatively good magnetic properties were obtained by adjusting the process conditions.•Constructed and validated an approximate relational model describing the correlation of defects and magnetic properties.