The invention discloses a cavity-based dual-band filtering balun, which includes a first cavity resonator and a second cavity resonator which are connected by a metal plate, the first cavity resonator is provided with an input PCB board, a metal ground layer of the input PCB board is provided with an input through line, the other side of the input PCB board is provided with an input microstrip line, and the first cavity resonator is provided with an input slot corresponding to a position of the input through line; and two opposite outside surfaces of the second cavity resonator which are adjacent to the metal plate are each provided with an output PCB board, metal ground layers of the two output PCB boards are respectively provided with an output through line, the other sides of the two output PCB boards are each provided with an output microstrip line, and the second cavity resonator is provided with an output slot corresponding to a position of the output through line and communicated with the output through line. A main body of the dual-band filtering balun includes two cavity resonators, its structure is high in quality factor and low in insertion loss, and meanwhile, the requirement of two passbands is realized by using two fundamental modes of the cavity resonators, thus reducing a size of a circuit.