Directional heat treatment reduces the number of transverse grain boundaries in pure copper wires at suitable temperatures, thereby promoting the formation of columnar or even single-crystal structures. This process significantly enhances the electrical conductivity of the wires and has become a research focus. Fundamentally, directional heat treatment is a secondary recrystallization process, involving key microstructural evolutions such as grain growth and grain boundary migration. Investigating its mechanism in pure copper wires is essential for optimizing their conductive performance. In this study, pure copper wires were subjected to directional heat treatment and systematically characterized using electron backscatter diffraction (EBSD). The effects of treatment on grain growth and boundary migration were analyzed, clarifying the evolution of grain boundary structures and crystallographic textures during columnar grain development. It was revealed that grains with a orientation preferentially develop into columnar structures, with most inter-columnar grain boundaries being low-energy ∑ 3 and ∑ 9 types. The novelty of this work lies in revealing the mechanism of directional grain boundary migration in pure copper wires and elucidating the formation mechanism of island grains after directional heat treatment.