Sewage treatment agent adding device

The invention provides a sewage treatment agent adding device, which comprises a sewage treatment pond, a water inlet pipe, a flow velocity detection mechanism, a track mechanism, a moving trolley and an agent supplementing mechanism, wherein the track mechanism comprises a rectangular frame, a step plate, a metal plate and an extension spring, sewage is conveyed into the sewage treatment pond through the water inlet pipe, the movable trolley moves on the track mechanism to achieve agent feeding, the flow velocity detection mechanism comprises a stress plate, a driving magnet, a fixing plate, a reset spring, a mounting box, a battery pack, a first slide rheostat and a first magnet, and the battery pack, the first slide rheostat and the first magnet are located in the mounting box, when the sewage flow is increased, the flow velocity detection mechanism can change the electric energy received by an electromagnet so as to make the electromagnet attract the metal plate to move upwards by a higher height, more se