Model discloses the flocculation mixer for water purification, sewage treatment, sedimentation tank which comprises a motor speed reducer, a transmission shaft, a baffle plate, an impeller, a guide cylinder and a supporting leg, a motor speed reducer is fixed on the frame, the speed reducer driving motor is connected with a transmission shaft, the impeller is installed on the driving shaft and is located in the the draft tube, the draft tube connected to the lower part of the leg, on the impeller blades from the hub position of the impeller along the radial extension; the width of the leaf from the root to the outer end of decreasing.