The utility model relates to a fluidized bed reactor with classification baffles, in particular to a fluidized bed reactor system. The fluidized bed reactor system is used for producing dimethylbenzene by alkylation reaction; the alkylation reaction comprises the process of enabling an alkylating agent to be in contact with aromatic hydrocarbons selected from benzene, toluene and a mixture of the benzene and the toluene under the condition of existence of a catalyst for promoting the alkylation reaction; the fluidized bed reactor system comprises a fluidized bed reactor with a plurality of injection stage parts; and the injection stage parts are used for injecting the alkylating agent and at least one of the aromatic hydrocarbons in a classifying manner, wherein the injection stage parts are separated by baffle materials and the baffle materials are suitable for reducing at least one of gas-phase backmixing, the bypass phenomenon and the bubble size in the process of producing the dimethylbenzene by the alkylation reaction. The fluidized bed reactor system has the improvement that reactants are injected in a classifying manner, wherein the stage parts are separated by structural fillers, so that at least one of gas-phase backmixing, the bypass phenomenon and the bubble size is minimized.