Abstract: To satisfy the great requirement of underwater operations, underwater flux-cored wire arc cutting (FCAC) was conducted. The effect of cutting voltage, cutting current and cutting speed on the shape of cut cavity was investigated, and the microstructure of heat affected zone (HAZ) was studied, simultaneously. The results indicate that the arc length and the wire extension are change all the time during the FCAC process. The width of lower part of the cut cavity is relatively larger than that of upper part; the width of cut cavity is increased with the increase of cutting voltage or cutting current. The width of lower part of the cut cavity is gradually decreased with the increase of cutting speed. At the same time, the heat affected zone, which contains re-melting zone, overheated zone, complete recrystallization zone, and incomplete recrystallization zone, is narrow due to the strong cooling effect in water environment.