Yarn-based strain sensor is an emerging candidate for the fabrication of wearable electronic devices. The intrinsic properties of yarn, such as excellent lightweight, flexibility, stitchability, and especially its highly stretchable performance, stand out the yarn-based strain sensor from conventional rigid sensors in detection of human body motions. Recent advances in conductive materials and fabrication methods of yarn-based strain sensors are well reviewed and discussed in this work. Coating techniques including dip-coating, layer by layer assemble, and chemical deposition for deposition of conductive layer on elastic filament were first introduced, and fabrication technology to incorporate conductive components into elastic matrix via melt extrusion or wet spinning was reviewed afterwards. Especially, the recent advances of core–sheath/wrapping yarn strain sensor as-fabricated by traditional spinning technique were well summarized. Finally, promising perspectives and challenges together with key points in the development of yarn strain sensors were presented for future endeavor.