The almost inevitable crystallization is a key hindrance to the excellent performance of additive manufacturing (AM) fabricated Fe-based metallic glasses (FMGs). Considering the role of chemical composition in glass-forming ability, ternary FMGs FeCuNi were selected to study the crystallization mechanism at an atomic level. The high inclination of crystallization in AM-fabricated FeCuNi FMG was obviously inhibited with increasing Ni addition until 30%, which lies in the decreasing emerging body-centered cubic phases, is correlated to the decreasing crystal bond pairs 1661 and 1441 and correspondingly decreasing Voronoi polyhedrons〈0, 6, 0, 8〉and〈0, 5, 2, 6〉. Meanwhile, the weakening crystallization is also indicated by the increasing amorphous phases such as the icosahedron and icosahedral-like polyhedrons. This work helps better understanding the weakening crystallization in AM-fabricated ternary or multi-component alloys, which is very important for achieving complex geometry FMG parts with less crystallization and, in turn, excellent performance by AM technique.