Abstract：Inspired by human skin, wearable electronics with self-healing capabilities and inherent sustainability have gained significant attention in recent years, putting forward an urgent need for tough and self-healing elastomers. Although various self-healing elastomers and wearable sensors have been designed and reported, there are still great challenges to synergistically improving their mechanical and self-healing performances. In this study, the self-healing polyurethane (SHPU) elastomer and carbon nanotubes/SHPU (CNTs/SHPU) fiber-based strain sensor with synergistically improved mechanical and self-healing properties were prepared by introducing the reversible non-covalent bonds and covalent cross-linking networks on the PU molecular chains and designing the structure of CNTs/SHPU fibers. Benefit from the synergistic strategy, the tensile strength of SHPU is as high as 36.2 MPa, the strain at break is 1086 %, the self-healing efficiency of stress and strain are 94.4 % and 98.0 %, respectively. Correspondingly, the tensile strength and strain of CNTs/SHPU fiber used for strain sensor is 21.9 MPa and 1412 %, respectively. These are typically high values compared with other self-healing elastomers and fibers reported previously. Besides, the conductivity of CNTs/SHPU fiber is almost unchanged after it is cut off and self-repaired. Benefit from the innovative self-encapsulation structure, the fiber-based tensile sensor exhibits excellent solvent resistance and sensing stability. It can be integrated into wearable devices through weaving technology to monitor the movement of human body. All of these excellent performances demonstrate that the tough and self-healing elastomer and its fiber-based self-encapsulating strain sensor have great potentials as advanced electronic sensors.