The invention discloses a method for treating heavy metal wastewater through a bacillus mucilaginosus polysaccharide and chitosan double-component flocculant and belongs to the technical field of wastewater treatment. The method comprises steps as follows: 1) selection: bacillus mucilaginosus is selected as a producing strain and preserved in the CGMCC (China General Microbiological Culture Collection Center) of the microbiological culture preservation management committee with the preservation number CGMCC 5766; 2) strain activation and ferment cultivation: a seed medium is inoculated with the strain for cultivation after the strain is activated by a selective medium, and seed fungi are obtained; a liquid fermentation medium is inoculated with the seed fungi for fermentation, and a fermentation broth containing bacillus mucilaginosus polysaccharides is obtained; 3) preparation of the double-component flocculant: a bacillus mucilaginosus polysaccharide component and a chitosan component are mixed uniformly in proportion, and the double-component flocculant is obtained; 4) treatment of the heavy metal wastewater: the double-component flocculant is added to the heavy metal wastewater in the volume ratio being 0.1%-10%, the mixture is stirred at the rotating speed of 300-500 rpm for 5-15 min, after full flocculation is observed, sedimentation is performed, flocculate is removed, and purified wastewater is obtained. After the wastewater is treated with the method, the turbidity of a liquid is reduced by 80% or more, Pb<2+>, Ni<2+> and Fe<3+> are reduced by 90% or more, and Zn<2+> and Cu<2+> are reduced by 80% or more.