Abstract: Transmission line method is extended to include multi-mode transverse electric （TE） of cavity modes which are introduced by aperture coupling and it is used to analyze the shielding effectiveness （SE） of double layer rectangular enclosure with aperture array. The electric SE of single layer with apertures is compared with that of double layer with apertures. The simulation results show that SE can be improved greatly with double layer shielding and it is worse on the resonance frequency of cavity modes whether in double layer shielding cavity or in single layer shielding cavity. The multi-mode transmission line method is revised when there are similar apertures in one face of the enclosure. Further discuss shows： for the same area of total apertures, SE is improved when the number of apertures increases; and the improved extent by increasing number of apertures in double layer shielding enclosure is greater than that in single layer shielding enclosure. The changing location of inner aperture along the axis of cavity does not affect SE greatly, and SE increases with the increasing size of cavity.