Conventional electrochromic smart windows primarily control solar transmittance but offer limited regulation of mid-far-infrared radiative heat exchange. Here, we report an all-solid-state multispectral electrochromic smart window (MSECW) integrating synergistic solar-infrared control, cross-band decoupling, and spectrally selective thermal emission. The 1.26 μm-thick ITO/WO₃/LiNbO₃/NiO/ITO multilayer stack was fabricated on glass via an integrated, all-vacuum magnetron sputtering process. Li⁺-insertion-induced localized surface plasmon resonance in WO₃ nanocrystals, combined with multilayer nanophotonic design, enables high emissivity within the 3-5 and 8-13 μm atmospheric windows in the cooling states while maintaining low emissivity outside these windows. Reversible switching between bright-warm (high solar transmittance/low infrared emissivity) and dark-cool (low solar transmittance/high selective infrared emissivity) modes enables solar heat gain and radiative heat exchange to synergistically support heating or cooling. The lower voltage threshold for infrared modulation further enables a bright-cool mode that preserves daylight transmission while enhancing radiative cooling. At ±2 V, the MSECW achieves an average solar-transmittance modulation of 0.56 and peak emissivity modulations of 0.43 at 3.9 μm and 0.49 at 9.2 μm. Significant optical modulation is retained after more than 6000 switching cycles. Outdoor experiments demonstrate a maximum chamber-temperature difference of 7.6℃ between the bright-warm and dark-cool modes and 4.6℃ between the two bright modes. EnergyPlus simulations across 11 cities predict annual HVAC energy savings of up to 86.6 MJ m^-2 relative to a reference window. This work provides a promising strategy for climate-adaptive building thermal management through coordinated multispectral regulation.