The invention discloses a salt-leaching system and a salt-leaching method for soil in saline-alkali soil. The system comprises a to-be-flushed plot and drainage ditches in two sides of the to-be-flushed plot. A large groove matched with each drainage ditch is formed in the bottom of the drainage ditch. A fresh water storage pond is arranged along the length direction of the large slot. A column isarranged at the bottom of the large slot. A small slot is formed in the top end of the column. The fresh water storage pond is lower than the small slot. A water pump is arranged in the fresh water storage pond. The water outlet of the water pump is connected to a drop irrigation pipe arranged in the to-be-flushed plot through a water conveying pipe. A flow drop film is paved on the top of each drainage ditch and sinks downward, the lowest sinking end of the flow drop film corresponds to the position of the fresh water storage pond, and the flow drop film is fixed to the small slot and is fixed and tightened. In an actual salt-leaching process, continuous circular salt leaching can be carried out after primary drainage salt leaching, so that an effect of multiple times of salt leaching byflooding once is achieved.