A water tank-less toilet flushing system includes a toilet bowl and a control system which includes a flush valve located higher than a top surface of the toilet bowl and a check valve operatively linked to the flush valve. When the flush valve is opened, the check valve is closed due to a water pressure for enabling the water to flush the toilet bowl. When the flush valve is closed, the check valve is opened for communicating an interior of the flush valve with an ambient atmosphere to prevent water in the toilet bowl to be backflow to the flush valve.