The invention discloses an ultra-wide-band Balun filter based on slot lines. The filter includes a metal grounding plate (5) fully coating the lower surface of a rectangular dielectric substrate (6), an input port feed line (1) coating the upper surface of the dielectric substrate (6), a first output port feed line (21), and a second output port feed line (22), a first F type slot line resonator (3) and a second F type slot line resonator (4) that are mutually in central symmetry are etched on the metal grounding plate (5), and the first output port feed line (21) and the second output port feed line (22) are in axial symmetry relative to the vertical arm of the second F type slot line resonator (4). The Balun filter is simple in structure and wide in bandwidth.