The invention belongs to the technical field of hydrometallurgy, particularly relates to a method for preventing ore heap hardening, and aims to prevent metals and impurities in leach liquor from forming insoluble precipitate in a heap and solve the problems of ore heap hardening, permeability lowering and the like by means of increasing the spraying amount and spraying acidity, optimizing a spraying system and the like. The method is characterized by comprising heap wetting, ore heap acidification period treatment, heap leaching medium-term treatment and leaching post-treatment. According to the method, ore is fully wetted with clear water before leaching, so that the residence time of an acidification-period high-concentration solution on the surface of ore is shortened, and secondary precipitation of leaching matters is relieved; high spraying strength is adopted at an ore heap acidification period, so that the thickness of a liquid film on the surface of the ore is reduced, and the ore leaching strength is enhanced; the sulfuric acid concentration of spraying liquid is kept constant at a heap leaching medium period, so that the spraying amount of a leaching agent is reduced gradually, the leaching process is enhanced, the metal concentration of the leaching liquor is increased, smooth proceeding of heap leaching is ensured, and the leaching period is shortened.