Using numerical approaches, two different mechanisms leading to enhanced transmission in a sandwiched nanofilm are demonstrated. The film is composed of a flat silver layer and two layers of silver prisms arrays on its both sides. The central flat silver layer is coated with glass substrates on its both sides and the silver prisms arrays are deposited on the glass layers. In the calculations, two different mechanisms leading to enhanced transmission are found. One mechanism follows the conventional believing in which the resonance wavelength depends on the neighboring distance between silver prisms in the array. The enhancement is due to the coupling of propagating surface plasmon polaritons (SPPs). In another mechanism, the resonance wavelength depends on the distance between the silver prisms array and the flat film rather than the neighboring distance between silver prisms in the array. The enhancement is due to the localized surface plasmons instead of propagating SPPs. By changing the thickness of the glass layers, these two mechanisms can also work cooperatively. Parameters that affect the enhanced transmission of the sandwiched nanofilm were also briefly studied.interference of diffracted evanescent waves generated at the subwavelength surface structures, such as holes, slits, or grooves. To explain similar enhanced transmission occurred for a metal film with a periodic array of slits, Takakuru studied the interaction of transverse magnetic-polarized light with a single slit and slits array, [6] Fabry-Pérot-like modes were also used to interpret the EOT phenomenon, where the transmission resonances arise from the setting up of the standing waves in each slit cavity. [7] However, these debates do not limit its applications in many different fields, such as photolithography, [8] optical filters, [9] and optoelectronic devices. [10] While, the presence of holes in a film is not necessary to achieve enhanced transmission. [11] Bonod et al. predicted that EOT could also be found in a continuous metal film as long as it is properly modulated. [12] Several groups have theoretically or experimentally demonstrated that a continuous metal film with nanoslits, [13] nanoridges, [14,15] or other periodically arranged nanostructures [16] shows a similar enhanced transmission feature with that of a perforated metal film, including the sharp Fano-shaped resonance feature. In optoelectric field, the extremely enhanced transmission for a metal film is also named as optical transparency. Continuous metal film has more promising applications in optics and plasmons due to its high electronic conductance when compared with that of metal film with holes, however, the applications are limited by its natural-opacity property. The enhanced transmission for a continuous metal film without holes has sparked the interest from many groups. Zayats and co-workers studied the enhanced transmission of continuous metal films coated with periodic metal or dielectric ridges on one or both interfaces using numerical methods, where the en...