The invention discloses an additive for a crystalline silicon polishing solution, and the additive is composed in parts by weight: 2-5 parts of alkyl indican, 1-3 parts of pyrazine, 0.5-2 parts of polyethylene glycol and 100 parts of water. In the process of carrying out surface polishing on silicon wafers, the additive disclosed by the invention is added into an alkaline solution, so that an excellent polishing effect can be achieved.