Abstract: A water drain accelerating device has a base with a discharge port connected to a flush way assembled inside a water tank. An overflow hole is connected to the discharge port. An overflow pipe is plugged to the base. The bottom of the overflow pipe is connected to the overflow hole. A negative pressure pipe is connected to the overflow pipe. Negative pressure generates inside the overflow pipe when the base is draining. Water inside the water tank flows out of the discharge port when water drains. The water level inside the cavity of the negative pressure pipe falls down with the water level inside the water tank. Negative pressure generates inside the overflow pipe, so air inside the overflow pipe can't enter into the discharge port through the overflow hole. An air pipe extends from the overflow hole to the flush way.