The invention discloses a water flushing method of a closestool. The closestool is equipped with a water storage pond. An injection water drainage port and a washing water drainage port are arranged in the water storage pond. A water inlet valve, a water drainage valve and a switching valve are installed in the water storage pond. The water flushing method comprises the following steps: A, water in the water storage pond is discharged out of the injection water drainage port while the water drainage valve is opened so that an injection water source is provided for flushing of the closestool; the water inlet valve and the switching valve are opened; water of water pipes outside can directly flow into the switching valve through the water inlet valve; then, water in the switching valve is discharged into a washing injection port so as to provide a washing water source for flushing of the closestool; B, according to the pre-set condition, the water drainage valve and the switching valve are closed; after flushing is stopped, outside water sources can flow into the water storage pond for standby use by the water inlet valve. With the water flushing method, an injection water source isseparated from a washing water source. No impact of divergent flows is caused between two water flows so that water flushing power is enhanced.