The invention provides a method for recycling waste acid generated in production of sulfuric acid from smelting flue gas. The method comprises the following steps: reducing waste acid by using Fe, performing evaporative crystallization to obtain FeSO4 crystals, enabling FeSO4 crystals to react with filter liquor, sulfuric acid and an oxidant generated in the activation step of producing activated clay from bentonite, so as to obtain polymeric aluminum ferric sulfate; selectively, enabling polymeric aluminum ferric sulfate to react with an organic flocculating agent, so as to obtain an organic-inorganic composite flocculating agent. According to the recycling method, the waste acid generated in the production process of sulfuric acid from smelting flue gas is adopted as a main raw material, and waste heat of smelting flue gas is utilized to produce the activated clay and the organic-inorganic composite flocculating agent which have broad markets in various industries, so that the problems about recovery of waste heat of high-temperature flue gas, treatment of waste acid, and seasonal storage of by-product sulfuric acid are solved; besides, plenty of valuable industrial products can also be produced; therefore, the method has quite high social benefit, environmental benefit and economic benefit.