The invention discloses a dynamic inlet/outlet sealing device for a heat treatment furnace in a protective atmosphere. According to the dynamic sealing device, metal strips can smoothly enter the heat treatment furnace in the protective atmosphere, and reducing gases in the hearth can be separated from the atmosphere. The device consists of a sealing roller, a sealing wedge, a transition wedge, a baffle, a sealing chamber, a protective gas inlet, a vertical cylinder, a bolt, a horizontal cylinder and a connecting body. The device can seal metal strips of different widths and thicknesses in a gapless mode and is particularly suitable for gapless dynamic seal on hot rolling strip steel with rough surfaces in the continuous reduction process. Moreover, according to the device, the size of the sealing caliber can be continuously and dynamically adjusted in the production process. The dynamic inlet/outlet sealing device is simple in manufacturing cost of equipment, simple in structure, convenient to detach and dynamic in adjustment.