The invention relates to a cavity filter, which comprises a shielding box, at least one separation wall, at least two resonant cavities, an input device and an output device. The separation wall is arranged in the shielding box; the separation wall is provided with a slot opening which is arranged at the top of the separation wall; the resonant cavities are arranged in the shielding box in the preset sequence; the two adjacent resonant cavities are separated by one separation wall; each resonant cavity is provided with a harmonic oscillator; one end of the harmonic oscillator is fixed on the inner wall of the shielding box; the other end thereof extends into the resonant cavity; the input device and the output device are respectively arranged in the resonant cavity of the first level and the resonant cavity of the last level; one end of the input device and the output device is electrically connected with the inner wall of the shielding box; the other ends thereof extend into the resonant cavity; and the harmonic oscillator comprises a support body and a carbon nanotube structure which is arranged on the surface of the support body.