The invention discloses an automatic feeding and discharging device for salt brine. The device includes a U-shaped water through tank formed in a pool ridge between the upstream and the downstream, the U-shaped water through tank is provided with a hinged rotation shaft, a lower cross beam is arranged below the U-shaped water through tank, the rotation shat is provided with a circular continuous flashboard, the circular continuous flashboard is uniformly provided with three flashboard bodies in the axial direction, one side of the circular continuous flashboard is provided with a switch lock pin rotating disc, three positioning grooves are uniformly formed in the switch lock pin rotating disc, and switching gate lock pins and water positioning lock pins are arranged at the positioning grooves; one side of the U-shaped water through tank is provided with a buoy with an additional weight, and the buoy is connected with the switching gate lock pins and the water positioning lock pins through cables respectively. The device has the advantages that workers do not need to manually observe the water level, a flashboard can be automatically and accurately opened and closed according to theset water level, the labor intensity is reduced, and the work efficiency is improved.