The invention discloses a toilet bowl drainage system. A toilet bowl comprises a seat brushing water way for flushing the inner wall of a toilet bowl and a main flushing channel communicated with thebottom of the toilet bowl. The drainage system comprises a water tank for storing flushing water, a water supply unit for supplying flushing water to the water tank, and a drainage mechanism comprising a valve core for opening or closing a drainage channel, wherein the water tank is provided with the drainage channel communicated with the inner cavity of the water tank and the main flushing channel, the valve core moves under the hydraulic effect and then opens the drainage channel, and the water supply unit supplies water to the seat brushing water way before the valve core opens the drainagechannel. Flushing of the inner wall of the toilet bowl happens before main flushing of a sewage discharge pipe, dirt on the inner wall of the toilet bowl can be flushed away by the main flushing channel, and therefore the toilet bowl can be brushed more thoroughly.