A new type of how visualization method utilizing a smoke-wire, a high-speed camera with high framing rates and a laser light sheet was employed to delineate the unsteady processes of large-scale vortices in the separated shear layer about a blunt-faced hat plate at Re-H = 560. The sequential images showed that the unsteady behavior of large-scale vortices in the separated shear layer varies as the shedding phases of large-scale vortices alter. Particularly, at a certain phase, a vortex-merging process between the two neighboring large-scale vortices took place.