The invention discloses a sedimentation tank water treatment suction dredger. The sedimentation tank water treatment suction dredger comprises a driving mechanism which is provided with a transmission shaft inserted to the bottom of the above tank, and also comprises a mud suction tube arranged at the tank bottom, and the mud suction tube is connected with the transmission shaft; a group of mud suction holes are distributed in the mud suction tube; and the bottom of the mud suction tube is provided with a mud discharge tube communicating with the mud suction tube, and the apertures of the mud suction holes gradually decreases from the edge of the tank to the center of the tank. The sedimentation tank water treatment suction dredger effectively solves the problems of non-uniform mud suction, easiness in pipeline obstruction, and occupation of too much space of the sedimentation tank in the mud discharge process of existing sedimentation tanks.