The invention aims at providing a polymeric ferric sulfate automatic feeding system with advantages of simple structure and convenient operation, and a method thereof. The invention adopts a technical scheme that: the polymeric ferric sulfate automatic feeding system comprises a reversed U-shaped hollow guide pipe and a support mechanism; the inlet end face of the reversed U-shaped hollow guide pipe is higher than the outlet end face; a slide device is arranged on a vertical guide pipe at the inlet end; a floating pad is arranged closed to the inlet end; the support mechanism comprises a vertical guide rail and a fixed support; the vertical guide rail is connected on the fixed support; the slide device arranged on the reversed U-shaped hollow guide pipe is connected with the vertical guide rail of the support mechanism; when the floating pad moves up and down with the solution volume, the slide device performs elevation movements on the vertical guide rail.