In order to clarify the behavior of inclusions in 15-7PH stainless steel and further improve its cleanliness, the consumable electrodes were prepared by UHP electric arc furnace→AOD decarburization→LF refining→mold casting process, and remelted by gas shielded electroslag remelting furnace with voltage swing control. The changes of oxygen and nitrogen before and after electroslag remelting were analyzed by HORIBA gas analyzer. The size, number, chemical composition and morphology of inclusions were analyzed by ASPEX SEM. It was found that the content of oxygen and nitrogen in 15-7PH stainless steel decreased slightly after electroslag remelting, and there was little change in the composition of inclusions, which were mainly composed of nitride inclusions (AlN, TiN), nitride/oxide composite inclusions, oxide inclusions and sulfide-oxygen/nitride inclusions. Among them, nitride inclusions had the largest size and quantity, which were significantly higher than other inclusions, and were worthy of special attention. Electroslag remelting had an obvious effect on the number and size of inclusions. After remelting, the number of inclusions increased greatly, especially nitrides. However, large inclusions were significantly reduced. The main reason for the large amount of nitride inclusions was the high content of Al, Ti, N in the steel. During the electroslag process, due to the adsorption of slag and the dissolution of some nitrides, the large inclusions were reduced, and the rapid cooling in the remelting process inhibited the growth of inclusions which led to the small size but increased of the number of inclusions in the electroslag ingot.