The invention discloses an aerator for sewage treatment. The aerator comprises a cell body, a plurality of racks, a bracket, a power unit and a plurality of mixing parts, wherein a guide rail is arranged on the cell body and is distributed in the length direction of the cell body; the plurality of racks are arranged on the cell body and the racks are distributed in the length direction of the cell body; the bracket is slidably arranged on the guide rail; the power unit is used for driving the bracket to move in the length direction of the guide rail; the plurality of mixing parts correspond to the plurality of racks one by one; each mixing part comprises a stirring shaft, a gear and a stirring blade; each stirring shaft is vertically and rotatably arranged on the bracket; each gear is mounted on the corresponding stirring shaft and is matched with the corresponding rack, the rack is located on the first movement path of the gear, and when the gear moves along the first movement path and is contacted with the corresponding rack, the rack drives the gear to rotate.