A cavity filter includes a housing, a plurality of resonators received in the housing, a cover covering the opening, a sliding plate, and a plurality of tuning posts. The housing defines an opening and comprises at least one pair of positioning portions. The plurality of tuning posts are fixed in the cover corresponding to the plurality of resonators. The sliding plate is disposed between the cover and the plurality of resonators, and is slidably positioned at the at least one pair of positioning portions. The sliding plate comprises a plurality of tuning cells and at least one elastic arm. The plurality of tuning cells is coated with a metallic layer and corresponds to the plurality of resonators. The at least one elastic arm extends from the sliding plate and elastically resists the cover.