Abstract: Using 304 austenitic stainless steel as the research object, the electroslag remelting experiment was carried out based on the self-designed low-frequency power electroslag furnace. The influence of power frequency on electroslag ingot density and Cr element distribution was analyzed by using the in-situ analysis technology, and the influence of low frequency electroslag remelting on electroslag ingot solidification structure and its mechanism were studied. The results show that the low frequency operation can make the density distribution of the electroslag ingot more uniform, but not the lower the frequency is, the better. When the frequency drops to 0.1 Hz, the non-uniformity of density distribution increases. The frequency has little effect on the maximum segregation of Cr element in the electroslag ingot. With the decrease of frequency, the angle between the temperature gradient and the vertical direction gradually decreases, and the depth of the metal pool becomes shallow. When the frequency drops to 0.4 Hz, the angle between the temperature gradient and the vertical direction is the smallest, about 20°, the columnar crystal is close to the axial growth, and the depth of the molten pool is the shallowest, with a shallow flat distribution. When the frequency drops to 0.1 Hz, the radial growth trend of columnar crystal increases, and the depth of molten pool increases. Compared with the traditional power frequency electroslag remelting, a reasonable remelting frequency can better stir the slag pool, promote a more uniform temperature distribution of the slag–metal interface and all parts of the molten pool, and reduce the depth of the metal pool. However, if the frequency is too low, the depth of the metal pool will be deepened.