The invention discloses a medicine adding device for sewage treatment. The device comprises a support, a water storage tank is arranged at the top end of the support, a medicine barrel is fixed abovethe water storage tank, a medicine injecting nozzle is arranged on the top of the medicine barrel, a metering pump is installed under the medicine barrel, one end of the metering pump is connected with the medicine barrel through a first connecting pipe, the other end of the metering pump is connected with a drainage trough through a second connecting pipe, the drainage trough is obliquely arranged between the water storage tank and a stirring barrel, a water inlet is arranged on the top of the water storage tank, a stepping motor is installed at the top end of the stirring barrel, an output end of the stepping motor is fixed to a stirring shaft through a coupling, installation notches are formed in the outer side of the stirring shaft, and a stirring blade is connected with one end of each installation notch. According to the medicine adding device for sewage treatment, by arranging the drainage trough, a water flow flows into the stirring barrel through the drainage trough, meanwhile, a medicine is injected into a sink through the corresponding medicine barrel above the drainage trough to make medicine liquid evenly flow into the drainage trough, manual adding is not needed, andthe automation degree is high.