The invention discloses a sedimentation tank disinfection device for sewage treatment. A blanking device comprises a fan-shaped storage tank, and a disc located at a lower end of the fan-shaped storage tank. The fan-shaped storage tank is mounted on a track. A brush strip is arranged at the place where the lower end of the fan-shaped storage tank is in contact with a disc. The disc is mounted on the inner wall of a sedimentation tank and is divided into six equal fan sections. One of two adjacent fan sections is covered with a circular hole. Chlorine dioxide powder is stored through the fan-shaped storage tank. During the rotation of a stepper motor, the powder in the storage tank evenly falls into the sedimentation tank when rotating to the perforated fan section of the disc. Stirring blades are installed on the erected track in the sedimentation tank. When the stepper motor drives the track to rotate, the lead screw part of the track drives the stirring blades to rotate and rise suchthat the powder and sewage fully react.