The invention discloses a high security water-sealed tank. The high security water-sealed tank comprises a tank body; an air inlet pipe stretches into the tank body from the top; an exhaust pipe is arranged on the top of the tank body; a blow-down pipe is arranged at the bottom of the tank body, and an overflow pipe is arranged above the same side wall; a water supplementing pipe is arranged between the overflow pipe and the blow-down pipe; the air inlet pipe is sleeved with an air inlet pipe casing pipe; the top of the air inlet pipe casing pipe is provided with an air outlet; and a surpassing exhaust pipe is arranged between the air inlet pipe and the exhaust pipe. Compared with the prior art, when a downstream pipeline valve is closed, a three-phase separator cannot float up; and stored water in the water-sealed tank cannot be drained completely, and at most, part of the stored water is drained from the overflow pipe.