The invention provides a continuously-cast billet descaling device and a continuously-cast billet descaling method. The continuously-cast billet descaling device comprises a water tank, a descaling working area and a cleaning working area, wherein the water tank is divided into an upper side area and a lower side area through a filter baffle, wherein the upper side area is used for containing hard particles and water and the lower side area is used for containing water; in the descaling working area, the hard particles and the water in the upper side area are sprayed onto a continuously-cast billet in the descaling working area to descale the continuously-cast billet; and the cleaning working area is arranged behind the descaling working area, and in the cleaning working area, the water in the lower side area is sprayed onto the continuously-cast billet in the cleaning working area for cleaning. According to the continuously-cast billet descaling device provided by the invention, the descaling effect can be improved, the process is simple and other auxiliary equipment is not needed.