A phase factor was introduced into the wave function properly, and the correlation of the dipoles was taken into account by a semiclassical approach. Thus a successful explanation of the observability of quantum beat is obtained for various circumstances. Particularly, it has been made clear that there should be no single atom beat for the lower state splited cases, which removes the difficulty of semiclassical theory in explaining quantum beat. Therefore it has been shown that the semiclassical theory can rise to the challenge from quantum electrody namics in explaining quantum beat.