The marginal glass-forming ability (GFA) of a binary Ni–Zr system is an issue to be explained considering numerous bulk metallic glasses (BMGs) found in a Cu–Zr system. Using molecular dynamics, the structures and dynamics of Ni50Zr50metallic liquid and glass are investigated at the atomistic level. To achieve a well-relaxed glassy sample, a sub-Tgannealing method is applied and the final sample is closer to the experiments than the models prepared by continuous cooling. With the state-of-the-art structural analysis tools such as cluster alignment and pair-wise alignment methods, two glass-forming motifs with some mixed traits of a metastable B2 crystalline phase and a crystalline Ni-centered B33 motif are found to be dominant in the undercooled liquid and glass samples. A new chemical order characterization on each short-range order (SRO) structure is accomplished based on the cluster alignment method. The significant amount of the crystalline motif and the few icosahedra in the glassy sample deteriorate the GFA.