In the event of spontaneous outbreak of fire in a large enclosed space such as an atrium, it is necessary that the personnel can be safely evacuated, whereby, the faultless design of the smoke management system becomes important. The natural tendency to form smoke layers below the ceiling in the absence of properly balanced heat and gas distribution in the air convection, could make the phenomenon of smoke scattering complicated. This paper makes an investigation of smoke interface formation and diffusion characteristics in an atrium-like space under fire for the purpose of effective smoke control. The formation condition of smoke layer interface is deduced by applying the profile method to the state equations, which was also confirmed experimentally. The analysis of smoke diffusion takes into account of an anisotropic turbulent flow with the buoyancy effects included in the momentum, heat and smoke transfer equations with a few basic assumptions made on some smoke properties. From the results of the numerical calculation, it was clarified that by driving a smoke exhaust fan at the top of the atrium could effectively prevent the smoke diffusion.