A novel square cavity coupled metal waveguide structure is proposed, which is composed of two mutually perpendicular rectangular metal waveguides and a square resonant cavity connecting rectangular waveguides. The band-rejection filtering characteristics are realized by the plasma local characteristics of the square resonator, and the dual-port all-optical plasma switch is realized by multiplexing. The effects of the length, refractive index and resonance distance of the square cavity on the strong transmission characteristics were studied by the finite difference time domain method. The results show that the optical switch based on the square cavity coupled metal waveguide structure has better stop-band characteristics and transmission characteristics, and its maximum transmittance is 92%, the minimum stopband transmittance is 0.2%, and the working range is 607~785nm.