Ti₃C₂T_x nanosheets have attracted significant attention for their potential in electromagnetic wave absorption (EWA). However, their inherent self-stacking and exorbitant electrical conductivity inevitably lead to serious impedance mismatch, restricting their EWA application. Therefore, the optimization of impedance matching becomes crucial. In this work, we developed polymethyl methacrylate (PMMA)@Ti₃C₂T_x@SiO₂ composites with a sandwich-like core–shell structure by coating SiO₂ on PMMA@Ti₃C₂T_x. The results demonstrate that the superiority of the SiO₂ layer in combination with PMMA@Ti₃C₂T_x, outperforming other relative graded distribution structures and meeting the requirements of EWA equipment. The resulting PMMA@Ti₃C₂T_x@SiO₂ composites achieved a minimum reflection loss of −58.08 dB with a thickness of 1.9 mm, and an effective absorption bandwidth of 2.88 GHz. Mechanism analysis revealed that the structural design of SiO₂ layer not only optimized impedance matching, but also synergistically enhanced multiple loss mechanisms such as interfacial polarization and dipolar polarization. Therefore, this work provides valuable insights for the future preparation of high-performance electromagnetic wave absorbing Ti₃C₂T_x-based composites.