The invention relates to a device for separating silt of a waste plastic fragment, and further relates to a method for the separating silt of the waste plastic fragment. The device for the separating silt of the waste plastic fragment comprises a conical tank, a water inlet pipe, a water outlet and a silt-separation mesh, wherein the cone tank is integrally inverse conical, and a silt-discharging opening is arranged at the bottom of the cone tank; the water inlet pipe is put in the side wall of the conical tank and stretches into the silt-separation mesh, the water outlet is arranged on the cone tank; the silt-separation mesh for only the silt and impurities to pass through is arranged inside the cone tank, and the shape of the silt-separation mesh corresponds to the cone tank; and the waste plastic fragment eddies, rotates along with fluid in high speed, and is arranged inside the silt-separation mesh. The device and the method for separating the silt of the waste plastic fragment have the advantages of being simple in structure, convenient to operate, and capable of effectively achieving mechanization and continuity of the silt-and-fragment separation process and improving silt-and-fragment separation efficiency and effects, and belong to the technology of recycle and cleaning of waste plastic.