The explosive development of flexible precision electronic devices necessitates materials with ultrahigh electromagnetic interference shielding effectiveness (EMI SE) and excellent mechanical flexibility to suppress unnecessary electromagnetic radiation. Herein, we report a feasible strategy to fabricate a flexible and water-proof porous film for high-efficiency EMI shielding, by utilizing electroless plating of silver (Ag) with the assistance of polydopamine (PDA) and Sn2+ on a commercial nylon mesh (CNM), followed by razor-thin polydimethylsiloxane (PDMS) coating. Results indicate that the fabricated CNM/PDA/Ag/PDMS (CNMAAS) films exhibit continuous coating of Ag nanolayer, which imparts the films perfect electrical conductivity up to 168,060 S/m and ultrahigh EMI SE of up to 91.6 dB, with only 1.38 vol% of Ag loading and 100 μm thickness. The films also exhibit impressive EMI SE enhancement per unit filler and thickness (eg: 4078 dB/vol%/mm and 240.9 dB/wt%/mm for the CNMAAS2 film), owing to the increased interfacial polarization and the conduction loss. Outstanding EMI SE reliability is also achieved for the films, with retentions as high as 96% even suffering 5000 cycles of bending deformation, ascribing to the good mechanical flexibility of porous CNMAAS films. Finally, water-proof, breathable and antibacterial ability of the CNMAAS film were demonstrated. This work provides a facile approach to effectively design and fabricate conductive nanolayers for ultrahigh-performance EMI shielding materials that can be applied in flexible smart electronic devices.