The invention discloses a binding material for filling fine-grain tailings. The binding material is prepared by milling and mixing the following components in percentage by mass: 15-40% of belite-sulphate aluminum cement, 2-10% of gypsum, 2-8% of quick lime, 40-70% of superfine-grain slag powder, 2-10% of coal ash, 1-6% of activating agent, 0.1-0.5% of activating accelerant, 0.1-0.5% of coagulant, and 0.1-0.5% of water reducer, wherein the activating agent is Na2SiO3, the activating accelerant is sodium fluosilicate, and the coagulant is any one or a mixture of two or more of LiOH, LiCO3 and LiCl; and the water reducer is a naphthalene water reducer or a polycarboxylic acid water reducer. According to the binding material for filling the fine-grain tailings, the problems that -0.074-mm fine-grain tailings and high-silt-content tailings are difficultly solidified and are low in strength after being solidified, and the strength of a filling body can meet a strength requirement on cut and fill of a mine on the filling body by using the binding material; the liquidity of slurry can be improved, and roof-contacting performance of the filling body can be improved; and the water retention capacity can be improved, and the water seepage of the slurry is reduced.