Hierarchical surface micro- and nanostructures have attracted much attention in recent years due to their important roles in many applications. Among numerous techniques, ultrafast laser surface texturing technology has gained great success in recent years due to its flexibility and controllability in preparing large-area hierarchical micro- and nanostructures on a wide range of metal surfaces. However, recent studies have demonstrated that low-cost nanosecond (ns) lasers are also reliable tools to induce hierarchical micro- and nanostructures formation on metals, but the underlying formation mechanism is not yet understood. In this study, by observing the morphology evolution of surface structures, we proposed that the formation of surface hierarchical micro- and nanostructures originates from the accumulation of laser-induced resolidified materials and the redeposition of laser-induced plume. On one hand, our proposed mechanism explains the effect of laser pulse width on the morphology of surface structures, and, on the other hand, it explains some phenomena observed in other studies, which can benefit potential applications of this technology in different areas.