The invention provides a preparing and feeding method for flocculating agent, which is characterized in that the usual method of synthesizing the flocculating agent adopts alkaline water solution in normal temperature, wherein, the consistence of Na2O in alkaline water is 5 to 15g/l; the synthetic flocculating agent adopts the preparation and feeding in high consistence, and the adding in low consistence. The preparing and conveying consistence is 0.3 to 0.5 percent, and the adding consistence is 0.05 percent. Hot water of 80 to 90 DEG C is used for diluting before adding; the synthetic flocculating agent is added on an ore pulp pipe of a settling tank, the adding method of two point type is adopted. Through optimizing the preparing and adding method of the synthetic flocculating agent, the invention effectively improves the flocculating and settling effect for the synthetic flocculating agent, reduces the consumption of natural flocculating agent, and enables the consumption of the synthetic flocculating agent and the natural flocculating agent to reach the best technical and economic index. Besides, the separated and overflowed suspended matter keeps consistent quality under the control range.