An underflow type clarifying pond comprises a pond body provided with a vertical side wall and a bottom wall, and an underflow driving device, wherein the pond body comprises a clarifying settling area and an inclined plate area; a mud pit is arranged at the bottom of the clarifying settling area; a flocculation reaction unit casing is arranged inside the clarifying settling area, and is provided a top wall and a vertical side wall; the lower end of the flocculation reaction unit casing is provided with an opening; the underflow driving device comprises a diversion cylinder arranged inside the flocculation reaction unit casing; a plurality of diversion plates are connected between the diversion cylinder and the vertical side wall of the flocculation reaction unit casing; an underflow propeller is arranged inside the diversion cylinder; a flocculant adding uniform distributor and a raw water inlet pipe are arranged at the lower part of the underflow propeller. According to the underflow type clarifying pond provided by the utility model, the flocculation reaction unit casing and the diversion cylinder are positioned inside the clarifying settling area; the occupied area is effectively saved as the flocculation reaction unit casing does not occupy land independently; the water flow ascending speed of a clean water area at the upper part of the clarifying pond is high, so that the production efficiency is effectively improved, the flocculation effect is excellent, and the effluent water quality is stable.