The invention discloses a method for preparing an oxidized form polysilicic acid ferro-aluminum coagulant. The method includes the following steps that (1) a
sodium silicate solution is added to a dilute sulphuric acid solution under the stirring condition, the pH value is adjusted to acidity, and standing and
polymerization are conducted on the mixture to obtain low-
polymerization-degree activated
silicic acid; (2)
ferric sulfate and aluminum
sulfate are added to concentrated
sulfuric acid and water to prepare an acidic
sulfate ferro-aluminum solution; (3) low-
polymerization-degree activated
silicic acid and the acidic sulfate ferro-aluminum solution are mixed and stirred, an
oxidizing agent and additive are added, stirring is stopped, after standing and curing are conducted, a stabilizing agent is added, and then liquid products are obtained; (4) the liquid products are dried and grinded to obtain the
powder coagulant. The products prepared from the method combine the advantages of an iron coagulant and an aluminum coagulant, the defects of
polyaluminum chloride and
polyferric sulfate coagulants in the using process are overcome, and the products have the advantages of capable of integrating the polysilicic acid cementation, aggregation, adsorption and bridging effects, large in aluminum salt coagulant floc, good in decoloration performance, dense in
ferric salt coagulant floc, and high in
settling speed.