Abstract: Most filling stations add flocculant manually to accelerate settlement of tailings.In order to avoid waste of flocculant,the paper renovates the whole system based on Siemens S7-300PLC and existing agent-adding equipment of filling system,offers a solution that properly automatically feeds agets in the tailings settlement proess.The paper in detail introduces the agent addition ratio,agitation mixing,carrying and settlement and man-machine interaction of the automatic agent-adding system.The system has achieved satisfactory results in industrial application in Huibaoling Iron Mine,reducing work load and lower flocculant consumption by 3 %,saving cost by 146 000 yuan/a at the same filling amount.The research can be used as reference by similar mines.