The invention discloses a flocculating agent injecting and adding device for an internal soft silt layer of a silt storage yard or a fill area. The flocculating agent injecting and adding device comprises a motor, a stirring rod, a stirring head and a flocculating agent filling sleeve; the stirring rod is driven by the motor; the stirring head comprises a stirring shaft fixedly connected with a lower end of the stirring rod; a plurality of layers of propeller blades are arranged on the stirring shaft; the flocculating agent filling sleeve is sleeved outside the stirring rod, and two ends of the flocculating agent filling sleeve are hermetically and rotationally connected with the stirring rod respectively via a sealing end plate; a plurality of through holes are arranged on a sleeve wall of the flocculating agent filling sleeve; and a flocculating agent filling soft tube is connected on the sealing end plate on an upper end of the flocculating agent filling sleeve. In the invention, a flocculating agent is injected while rotating and stirring silt so that the uniformity of injection and the use efficiency of the flocculating agent are improved. The flocculating agent injecting and adding device disclosed by the invention has the advantages of a simple structure, light weight, simple and convenient operation, high efficiency and good reliability.