Asymmetric tilt boundaries on conventional twin boundaries (TBs) are significant for understanding the role of twins on coordinating plastic deformation in many metallic alloys. However, the formation modes of many asymmetric tilt boundaries are hard to be accounted for based on traditional theoretical models, and the corresponding solute segregation is complex. Herein, atomic structures of a specific asymmetric boundary on {1012} TBs were reveled using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), molecular dynamics (MD) and density functional theory (DFT) simulations. Reaction between <a₆₀>_M dislocations and the {1012} TB can generate a ~61°/25° asymmetric tilt boundary. The segregation of Gd and Zn atoms is closely related to the aggregated <a> dislocations and the interfacial interstices of the asymmetric tilt boundary, which is energetically favorable in reducing the total system energy.