This invention is a toilet flushing system. It consists of a button controlled pressure flushing device, a sealed water tank, a flushing valve, major and minor flushing control valves, an air induce device and a one-way water valve. The characteristic of the system is that the button controlled pressure flushing device has a water-volume adjustable valve, a flushing valve with a sealed cavity which has a water injection pipe and a water release pipe. The inlet and the outlet of the water-volume adjustable valve are connected to the outlet of the one-way water valve and water injection pipe of the flushing valve respectively. The inlets of the major and minor flushing control valve are connected to the water release pipe of the flushing valve. The outlets of the major and minor control valves are linked to the main release outlet which has large diameter and high speed on-off action. Compare with the existing pressure-assistant flushing system, its structure is simple and at the same times, the amount of water used in the minor flushing can be controlled by adjusting the flow difference between water-volume adjustable valve and the minor control valve.