Since smart materials and structures are highly pursued for their great advantages in self-adaptable, self-healing and self-recoverable capability upon environmental condition change, here we demonstrate hydro-sensitive smart sandwich structures with self-adaptable electromagnetic interference (EMI) shielding ability via constructing polymeric porous non-woven-based spacers into highly conductive pyrolytic graphite papers. The spacers play the critical role in tuning the electromagnetic response capability, leading to substantially varying the electromagnetic shielding performance of the sandwich structures upon various water loadings. With the presence of polar water molecules, the porous polymeric spacers were significantly changed via creating polar induced interfaces. According to the electromagnetic shielding performance at initial, wet and re-dried conditions, the results suggest two types of smart structures, namely EMI shielding function switchable and function enhanced EMI shielding structures, which promises a novel platform for designing hydro-stimulus smart materials and structures for electromagnetic response applications.