In recent years, stretchable and wearable strain sensors with excellent sensing performance are garnering significant research attention owing to their diverse range of application prospects in human activity monitoring, healthcare and biomedical engineering, and human–machine interaction. In this study, Rebound silicone elastomer/graphite nanoflake/Rebound silicone elastomer sandwich structured nanocomposites are constructed for strain monitoring and wearable applications. A cost-effective, environmentally benign, and scalable spray coating technique has been utilized to achieve highly conductive functional sensor materials by coating graphite nanoflakes onto the soft, epidermis-like, and highly elastic Rebound silicone elastomers. In strain monitoring, the Rebound silicone elastomer/graphite nanoflake (GNF)/Rebound silicone elastomer sandwich structured nanocomposite strain sensors demonstrate high performance with a large strain sensitivity (a maximum gauge factor of 96.73), a wide sensing range of up to 50%, a fast response and recovery speed (160 ms), high linearity, and prominent durability (more than 850 stretching-releasing cycles under an extensive tensile deformation of 15% strain). As a result, the Rebound silicone elastomer/graphite nanoflake/Rebound silicone elastomer sandwich structured nanocomposite strain sensor demonstrates attractive prospects in precision measurements of all frequencies of human activities, including tiny mechanical deformations (facial expressions, eye activities, blood flow pulse, and vibration of the vocal cords) and large-strain human joint movements (bending process of a finger, and wrist, elbow, and knee bending), hence exhibiting substantial potential in human activity monitoring as well as biomedical engineering.