The invention discloses a heavy-metal-polluted acidic soil repairing material as well as a preparation method and application thereof. The repairing material is prepared from the following raw materials in percentage by weight: 10-20% of biomass electric power plant ash, 10-20% of slag powder, 10-30% of steel slag powder, 5-10% of fly ash and 25-50% of bentonite by uniformly mixing in a dry powder state. The preparation method comprises the following steps of: firstly, drying the raw materials until the water content is smaller than or equal to 1%; then, respectively weighing the raw materials according to the percentage by weight; and finally, uniformly stirring. The in-situ repairing of heavy-metal-polluted acidic soil is achieved by covering a layer of repairing material on the soil surface, uniformly mixing the soil surface layer with the repairing material in plowing and stirring modes, and detecting the contents of Cd, Pb, Cr, Cu, Zn, Mn, Hg, As and Ni in the repaired soil and the soil pH value after 3-6 months until meeting the requirements of the second-level soil environment quality standard in GB15618-1995.