The invention discloses a flue gas desulfurization byproduct-based inorganic gelled material and a preparation method thereof. In the material, desulfurization ash generated in flue gas desulfurization treatment of a coal fired power plant is used as a main material; and slag, gypsum and cement clinker are mixed and ground with the main material to form the inorganic gelled material. The inorganic gelled material comprises the following components in percentage by weight: 30 to 40 percent of desulfurization ash, 45 to 55 percent of slag, 3 to 5 percent of gypsum and 8 to 12 percent of cement clinker. Because the desulfurization ash is used as a raw material for preparing the inorganic gelled material, no or little natural resource is used, and secondary pollution of the desulfurization ash is reduced. The preparation method comprises the steps of raw material selection, pre-grinding, mixing and grinding. Because the mechanical means is adopted, the raw materials do not need high-temperature calcination treatment, the manufacturing process is very compact, the production cost is extremely low, high energy consumption and high pollution caused by calcination can be avoided, the energy can be greatly saved, and the requirements of energy conservation and emission reduction are met. By detection, various inspection indexes of the inorganic gelled material meet the requirement of 22.5 strength level in GB / T3183-2003 Masonry Cement, and the inorganic gelled material can fully replace the traditional product.