The invention discloses a pressurized toilet flushing device, which comprises a water tank body (16), a one-way valve (7), a flushing switch (8), a water inlet control switch (6), a buoyancy tank (4)and a counterweight (5), and is characterized in that a bracket (15) is fixed in the water tank body, the upper part of the bracket is sleeved with a large driving gear (1) and a small driving gear (2) which are coaxial through a bearing seat and a driving shaft, a piston cylinder (11) is fixedly connected below the bracket, a piston rod (13) is fixed at the center of the upper surface of a piston(12), a driven rack (14) is fixedly connected with the piston rod, the driven rack is meshed with the small driving gear, one end of the inner part of the piston cylinder, near an outlet, is fixedlyconnected with a supporting plate (10) with a hole at the center, an inflatable air bag (9) is fixedly connected to the supporting plate, a driving rack (3) is fixed on the buoyancy tank, the drivingrack is meshed with the larger driving gear.