The invention relates to the field of wastewater treatment and provides a method for treating composite heavy-metal wastewater through coagulation-chemical precipitation. The method comprises the following steps: (1) detecting varieties and concentrations of heavy metals in the wastewater; (2) adding FeSO4 into the wastewater, and reducing Cr(VI) into Cr(III); (3) adjusting a pH value to an optimum range; (4) adding PFS for a coagulation-chemical precipitation reaction of a first stage; (5) adding Na2S into supernatant, carrying out a reaction with Hg, so as to produce HgS precipitates; (6) adjusting a pH value to an optimum range again; and (7) adding the PFS again for the coagulation-chemical precipitation reaction of a second stage. The method has the advantages that different heavy metals can be removed under the condition of optimal pH in a staged adding manner, the treatment effect is good, and a variety of heavy metals in the water can reach standards simultaneously; and the operation is simple and convenient, the cost is low, and a secondary pollution problem is absent.