The invention relates to an electromagnetic rotational flow water gap for continuous casting. The electromagnetic rotational flow water gap for continuous casting comprises a water gap pipe and an electromagnetic rotational flow device, wherein the electromagnetic rotational flow device is arranged around the middle area of the water gap pipe; the water gap pipe in a different-diameter structure comprises an upper part of the water gap pipe, the middle area of the water gap pipe and a molten steel outlet part; the sectional area of the middle area of the water gap pipe is 1.1-20 times the sectional area of the molten steel outlet part; the length of the middle area of the water gap pipe is 10-90% of the whole length of the water gap pipe; and the cross section of the middle area of the water gap pipe is a round, an oblong, a rectangle and a polygon with 1-20 sides. By enlarging the sectional area of the middle area of the water gap pipe, the electromagnetic rotational flow water gap for continuous casting adds the functional area of a magnetic field to the molten steel, increases a distance between magnetic poles of an externally arranged electromagnetic rotational flow device and improves efficiency of the magnetic field. The electromagnetic rotational flow water gap for continuous casting enables the molten steel in the water gap pipe to generate a relatively strong rotary force, solves bias flow phenomenon of the molten steel in the water gap pipe efficiently and is good for improving quality of steel billets.