The invention relates to a device and method for jointly removing sulphur, saltpeter and mercury by a semidry method through a circulating fluidized bed. The device comprises a flue and a circulating fluidized bed reaction tower which are sequentially connected, wherein the flue is connected with the bottom inlet of the circulating fluidized bed reaction tower and is also connected with an ozone generating device. Ozone is sprayed into the flue through an ozone distributor, NO and Hg<0> in the smoke are oxidized into high valence NOx and Hg<2+> in the flue, the oxidized smoke is sent to the circulating fluidized bed reaction tower, and SO2, high valence NOx and Hg<2+> in the smoke react with a Ca-based absorbent under the action of atomized water in the reaction tower so as to be removed. By utilizing the characteristics of simple system, good performance, small land occupation and less investment of the flue gas purification technology through the circulating fluidized bed by the semidry method, the multiple contaminants are jointly removed.