Benefiting from a specific multilayered structure, yolk–shell microspheres with void spaces are considered promising electromagnetic shielding materials which do well in enhancing the decay of electromagnetic waves. Commonly reported synthesis methods of yolk–shell nanostructures include sacrificial templates and tedious subsequential treatment. In this work, a novel, green and facile plasmolysis-inspired route was developed to fabricate uniform yolk–shell hydrogel-core@void@MXene-shell (poly(N-isopropylacrylamide)@void@polystyrene@MXene, abbreviated to PNIPAM@void@PS@Ti₃C₂T_x) nanocomposite microspheres. The void space between the PNIPAM core and the PS supporting layer was created on the basis of the shrinkage of the soft PNIPAM hydrogel core due to the removal of water in the hydrogel. In addition, a microsphere model was developed to predict that the void space can modulate the impedance matching to attenuate the reflection of electromagnetic waves on the surface of the microsphere and enhance the entry of electromagnetic waves. Ultrathin hydrogel-core@void@MXene-shell (PNIPAM@void@PS@Ti₃C₂T_x) self-supporting films could be prepared via filtration–drying of PNIPAM@PS@Ti₃C₂T_x nanocomposite microspheres. The 25 μm ultrathin nanocomposite film showed excellent electromagnetic interference (EMI) shielding effectiveness of 72 dB at 9.5 GHz and exhibited a wide absorption spectral range from 8.2 GHz to 12.4 GHz (>30 dB). The electromagnetic parameters of the equivalent medium model are obtained through the retrieval algorithm of the actually measured S-parameters, and models were constructed to simulate and explain the electromagnetic shielding performance.