A tunable filter includes a first waveguide body, a second waveguide body, a metal plate, a tuning piece, and a driving piece. A first cavity is disposed in the first waveguide body, and a second cavity is disposed in the second waveguide body. The metal plate is sandwiched between the first waveguide body and the second waveguide body, multiple windows are disposed on the metal plate, and the first cavity and the second cavity are in communication and are symmetrically distributed on both sides of the metal plate. The tuning piece includes a dielectric pull-rod and multiple metal sheets connected to the dielectric pull-rod, the dielectric pull-rod protrudes out of the first waveguide body and is connected to the driving piece, the multiple metal sheets are disposed inside the first cavity, and the multiple metal sheets are disposed corresponding to the multiple windows.