An embodiment of the present invention discloses a waveguide filter, which includes a first waveguide at an upper layer and a second waveguide at a lower layer. The first waveguide and the second waveguide are isolated from each other by a metal isolation layer. The first waveguide forms a first resonant cavity. The second waveguide forms a second resonant cavity. The first resonant cavity and the second resonant cavity overlap each other. A coupling slot is disposed at the metal isolation layer in an overlapping area.