The invention relates to a semi-continuous casting device. The semi-continuous casting device is composed of a liquid inlet, a heat preservation cover, a heat preservation cup, molten metal, a liquidguide pipe, an ultrasonic vibration rod, a protective cover, a platform, a protective gas pipe, a crystallizer, an electromagnetic coil, cooling water holes, crystallizer molten metal, a casting rod,a dummy ingot device, a flow limiting block, a heat preservation cup protective gas inlet pipe and the like. The semi-continuous casting device is used for semi-continuous casting of light alloys, gasprotection is adopted to prevent the molten metal from being oxidized, and electromagnetic stirring and ultrasonic vibration modes are adopted in the solidification process to jointly refine crystalgrains. According to the semi-continuous casting device, the defects that in a traditional semi-continuous casting process, the molten metal is prone to being oxidized, slagging and other factors damaging the quality of transmitted liquid are overcome, and the electromagnetic stirring and ultrasonic vibration combined mode is adopted in the casting rod solidification process, so that internal quality of the casting rod is better.