The utility model provides a water-sealed tank with a diversion cone at the bottom, which belongs to the technical field of water-sealed tanks. A cylindrical tank body (2) is provided with an air inlet pipe (1), an air outlet pipe (5), a water outlet/inlet (3) and an overflow port (4), wherein the air inlet pipe (1) is arranged on one side of the upper part of a cylindrical barrel; the water outlet/inlet (3) is formed at the bottom of the cylindrical tank body; an inflow air shunting plate (7) is arranged in the air inlet pipe, and is a shunting plate which is in downward smooth bending transition from the air outlet of the air inlet pipe; a barrel on the lower part of the air outlet pipe is provided with the overflow port (4); an outflow air shunting plate (8) is arranged in the air outlet pipe (5), and is in smooth bending transition on a curve in a streamline pipe; the bottom of the barrel is provided with a bottom diversion cone (6); the upper cone part of the bottom diversion cone is positioned in the air outlet pipe; and a gap is formed between the upper cone part and the air outlet pipe. The airtightness of the water-sealed tank is enhanced, the water-sealed tank is more reliable, and the operating cost of the water-sealed tank is lowered simultaneously.