This study presents a method for modulating the electromagnetic (EM) response of MXene/TiO₂ hybrids through in situ atomic reconstruction engineering, enabling the development of multifunctional EM devices that operate across multiple spectrums, including GHz, infrared, and visible light. The hybrids were synthesized by calcining Ti₃AlC₂ at different temperatures, resulting in MXene/TiO₂ hybrids with tunable conduction loss and polarization relaxation. These hybrids exhibit adjustable spectral responses in the GHz, infrared, and visible spectrums, allowing the construction of several EM devices. An antenna array demonstrates excellent EM energy harvesting in multiple microwave bands with |S₁₁| up to -63.2 dB and tunable performance by bending degree. An ultra-wideband bandpass filter achieves a passband of about 5.4 GHz and effectively suppresses EM signals in the stopband. An infrared stealth device has an emissivity of less than 0.2 in the infrared spectrum at wavelengths of 6–14 μm. The study highlights the potential of MXene/TiO₂ hybrid-based EM devices for applications in EM protection, wireless communication, and information transmission. The results demonstrate that in situ atomic reconstruction engineering effectively regulates the EM response of MXenes, enabling the design of multifunctional EM devices with multi-spectrum stealth capabilities. The work provides new insights for the development of EM functional materials and devices with multi-spectrum capabilities.This study presents a method for modulating the electromagnetic (EM) response of MXene/TiO₂ hybrids through in situ atomic reconstruction engineering, enabling the development of multifunctional EM devices that operate across multiple spectrums, including GHz, infrared, and visible light. The hybrids were synthesized by calcining Ti₃AlC₂ at different temperatures, resulting in MXene/TiO₂ hybrids with tunable conduction loss and polarization relaxation. These hybrids exhibit adjustable spectral responses in the GHz, infrared, and visible spectrums, allowing the construction of several EM devices. An antenna array demonstrates excellent EM energy harvesting in multiple microwave bands with |S₁₁| up to -63.2 dB and tunable performance by bending degree. An ultra-wideband bandpass filter achieves a passband of about 5.4 GHz and effectively suppresses EM signals in the stopband. An infrared stealth device has an emissivity of less than 0.2 in the infrared spectrum at wavelengths of 6–14 μm. The study highlights the potential of MXene/TiO₂ hybrid-based EM devices for applications in EM protection, wireless communication, and information transmission. The results demonstrate that in situ atomic reconstruction engineering effectively regulates the EM response of MXenes, enabling the design of multifunctional EM devices with multi-spectrum stealth capabilities. The work provides new insights for the development of EM functional materials and devices with multi-spectrum capabilities.