The utility model relates to a siphon type water-flushing device, particularly a pressing-water siphon water-flushing device. Water is filled in a water tank, and the water enters a water inlet pipe 1 and a water guide pipe 2. When the water rises to an upper hole D, a floating body opening E is sealed; a floating body 4 floats upwards. When the water height is h, the vertical and downward pressure is applied to the floating body 4; the floating body moves downwards. Under pressure, a middle hole C is sealed by a one-way valve 6; then, the water enters the water guide pipe 2. A connecting space V is filled with the water, and the water enters a water outlet pipe 3; a siphon phenomenon is formed, and the water flows into a toilet. Under water pressure and atmospheric pressure, the water which is stored rushes and opens the one-way valve 6; the water enters the water guide pipe 2. The water flows into a toilet through the connecting space V and the water outlet pipe 3; when the water storage level drops to the position of a lower hole B, the water stops.