The present invention discloses a method for preparing a light aromatic hydrocarbon through catalytic pyrolysis of a lignin fluidized bed, and belongs to the technical fields of environmental protection and energy. The present invention is characterized in that modified USY molecular sieve catalyst particles are used as a fluidizing medium, wherein a particle size of of the particles is 0.2-0.35 mm. A lignin raw material enters into a fluidized bed reactor filled with the hot fluidizing medium and comes into contact with the modified USY molecular sieve catalyst in a fluidized state so as to perform a rapid catalytic pyrolysis reaction at 400-550 DEG C. Pyrolysis products enter into a cyclone separator so as to separate out solid particles and the rest of the products enter into a condenser so as condense and separate out liquid products and gaseous products. The solid particles comprise the modified USY molecular sieve catalyst and coke. The solid particles enter into a catalyst regeneration tower. In the presence of excess oxygen, the coke on the surface of the modified USY molecular sieve is removed at 500 DEG C, and then the modified USY molecular sieve enters into the fluidized bed again to participate in a reaction. The method provided by the present invention is simple in process, and has good economic benefits as well as good industrial application prospects.