The invention discloses a treatment additive for silver-containing black silicon wastewater and a treatment method. The treatment additive comprises three additives as follows: an additive X1 which isone or a mixture of sodium chloride, sodium sulfide and sodium dimethyldithiocarbamate mixed in any ratio, an additive X2 which is one or a mixture of polyaluminum ferric chloride, polyferric sulfate, polyaluminium sulfate, polyferric chloride and polyaluminum ferric sulfate mixed in any ratio and an additive X3 which is one or a mixture of polyacrylic acid, sodium polyacrylate, calcium polyacrylate, styrene sulfonate, lignosulfonate, acrylic acid, methylacrylic acid and polyacrylamide mixed in any ratio. The additive can be subjected to a reaction rapidly with silver ions in the wastewater at room temperature to generate a chelate which is insoluble in water and has good chemical stability, so that heavy metal are caught and removed.