The invention discloses a concrete expansion agent containing circulating fluidized bed combustion coal solid sulfur clinker. The concrete expansion agent is characterized by comprising the following components in percentage by mass: 30 to 50 percent of solid sulfur clinker, 40 to 65 percent of anhydrite and 5 to 30 percent of lithium slag. During preparation, after the components are crushed andground, the components are taken according to the proportion and mixed uniformly to obtain a product without calcining. Because industrial wastes such as the solid sulfur clinker, the lithium slag and the like are used as main raw materials, the concrete expansion agent changes the wastes into valuable, has low cost, reduces environmental pollution, has simple production process, low energy consumption and good performance, and has market competitiveness and strong practicability compared with like products.