The invention relates to an aqueous vapor separation system of a vacuum cooling water tank for profile extrusion. The aqueous vapor separation system comprises a sealed tank body for aqueous vapor separation, a sealed vapor chamber, a negative pressure device, a water pump, an upper liquid level switch and a lower liquid level switch, wherein a plurality of vapor extraction openings which are communicated with a vapor extraction port of the vacuum cooling water tank are formed in the upper end of the sealed tank body; the sealed vapor chamber is arranged on the top of the sealed tank body; a vapor inlet is formed in the bottom of the sealed vapor chamber and is communicated with an inner cavity of the sealed tank body; the negative pressure device is used for extracting vapor from the sealed vapor chamber to form negative pressure; the water pump is used for pumping water settled at the lower part of the sealed tank body; the upper liquid level switch and the lower liquid level switch are arranged on the side wall of the sealed tank body and are used for controlling the water pump to intermittently pump the water settled at the lower part of the sealed tank body. The vacuum cooling water tank is slightly influenced by vacuum-pumping of the negative pressure device, so that the surface quality of a profile can be improved, the water pump intermittently works, power can be saved, and the service life can be prolonged.