One-dimensional (1D) yarn or fiber-based supercapacitors that have small diameter, volume and high mechanical strength are needed due to the demands on power source for wearable electronics, micro-devices, and implantable medical devices. The composite sheath is fabricated on a commercially available CNT yarn substrate by alternating depositions of MnO2 and Ag layers. Synergistic effect of high loading level of pseudocapacitive MnO2 and reasonably improved rate-capability are achieved. In the composite sheath, the interconnected networks provide electrical contact between MnO2 aggregates and adjacent Ag layer. The conductive Ag inter layers shorten the solid-state charge diffusion length in the MnO2. Moreover, generated electrons during the charge/discharge process can be collected rapidly by the adjacent Ag layer, therefore, the great extents of MnO2 could be loaded onto the surface of CNT core fiber electrode without a significant rate-capability degradation. Due to the high MnO2 loading level, the composite sheath-core yarn supercapacitor showed excellent specific areal capacitance (322.2 mF/cm2) and according energy density (18.3 µWh/cm2).