The atomic structure and dynamic behavior of the solid-liquid interface of alumina were observed in a transmission electron microscope (TEM). The in-situ heating experiment of the alumina powder was performed using the newly developed heating holder. The surface of alumina was partially melted at about 2000K. Molten alumina on the surface migrated along the surface and formed liquid droplets. Such droplets existed stably on the surface during observation. The solid-liquid interface was observed by high resolution electron microscopy. The layer-by-layer growth of solid was observed on the solid-liquid interface. The nucleation of the monolayer island and the progress of the atomic step were observed directly. The velocity of the step progress at the solid-liquid interface was directly measured.