The invention relates to a method and a device for producing an anionic surfactant through sulfonation of liquid SO3. The method provided by the invention has the characteristic of simple process. The device has the characteristic of low equipment requirement. According to the technical scheme, the method for producing the anionic surfactant through sulfonation of the liquid SO3 comprises the following steps in sequence: (1) adding organic materials into a liquid ring vacuum pump; (2) adding the liquid SO3 into an SO3 evaporating pot; (3) adding SO3 steam and the organic materials into a homogenizing pump to remove sulfonation reaction heat; (4) reacting sulfonate for preparing the anionic surfactant to obtain the anionic surfactant. A device for sulfonating with the liquid SO3 is characterized in that (1) the organic materials are added into a liquid inlet of the liquid ring vacuum pump, the liquid SO3 is input into the SO3 evaporating pot, and SO3 gas evaporated in the SO3 evaporating pot is introduced into an air suction port of the liquid ring vacuum pump at the same time; (2) the outlet of the liquid ring vacuum pump is connected with the homogenizing pump and a heat exchanger in sequence through a pipeline.