Harvesting low-grade heat from both human metabolism and environmental waste through thermoelectric fabrics offers a sustainable pathway for wearable power generation. However, a critical challenge exists in establishing substantial temperature differentials for continuous thermoelectric generation while maintaining physiologically comfortable skin temperatures in dynamically variable environments. Herein, we present a dynamic radiation-modulated sandwich-structured fabric capable of diurnally adaptive operation that simultaneously enables thermal comfort regulation and thermoelectric energy harvesting. Based on a parallel dual-spinneret blow-spinning technique, we engineer all-fibrous thermoelectric fabrics with asymmetric multi-walled carbon nanotube (MWCNT) and silver nanowire (AgNW) electrodes. The optimized sandwich fabric achieves an out-of-plane temperature gradient (ΔT) of 9 °C under 1 kW·m⁻² daytime solar irradiation and −5 °C at night (ambient temperature of 28 °C), while maintaining skin-contact temperatures within the physiological comfort range (35.5–38.3 °C). Theoretical and experimental studies reveal that these self-regulated bidirectional temperature gradients result from asymmetric optical absorption/emission properties between the MWCNT top layer (solar absorptance α_solar = 91%, mid-infrared emissivity ε_MIR = 87%) and the AgNW bottom layer (α_solar = 18%, ε_MIR = 20%). This effect is synergistically enhanced by the hierarchical porous fibrous interlayer with confined thermal transfer. Outdoor experiments demonstrate stable diurnal operation for thermal comfort and energy harvesting, generating a peak voltage of 20 mV through modular integration of sandwich fabrics.