Abstract: Because of the importance of the electromagnetic interference resistance in modern life， the shielding effectiveness of double-deck rectangular cavity with apertures irradiated by plane electromagnetic wave was modeled.In the modeling process，incident angle and polarization angle of the plane electromagnetic wave were introduced，and the scattering voltage produced on the aperture was taken as the radiation source.The aperture was taken as the asymmetrical coplanar stripline while the rectangular cavity as a rectangular waveguide with one end completely open and another end completely closed.The shielding effectiveness of any point in the cavity was calculated using transmission line theory.Compared to the former models， this method improves the completeness， computation speed，and the shielding effectiveness which supplies good reference for engineering practice.