A cavity filter having two series of resonance chambers bilaterally connected between an antenna port and two opposing signal input/output ports in a resonant space therein, each series of resonance chambers having the last resonance chamber thereof connected to the antenna port and the first resonance chamber thereof connected to the respective signal input/output port and kept in communication with the associating last resonance chamber through one respective channel and the second resonance chamber thereof kept in communication with the last second resonance chamber thereof through one respective channel to provide cross-coupling feedback, getting better stop-band flatness and improving signal quality.