Abstract: A new hot-top casting mold was developed on the basis of conventional hot-top casting, and the low-frequency (LF) electromagnetic field was applied in the process of casting. The stable technological conditions for hot-top casting of φ500 mm 7050 high-strength aluminum ingots were gotten, i.e. smooth ingots were available, when electromagnetic frequency is 15 Hz with electromagnetic intensity 10000 At. The microstructure of ingot samples were observed by Leica DMI microscope. Experimental results showed that the LF electromagnetic field can improve the surface quality of ingot with grain refining and internal cracks suppressed, and the reasons why the quality of ingots are improved and the effect of LF electromagnetic field on the shape of melt cave were summarized.