Hydrogels have attracted much attraction for promising flexible electronics due to the versatile tunability of the properties. However, there is still a big obstacle to balance between the multi-properties and performance of wearable electronics. Herein, we propose a salt-percolated nanocellulose composite hydrogel which was fabricated via radical polymerization with acrylic acid as polymer networks (NaCl-CNCs-PAA). CNCs were utilized as a reinforcing agent to enhance the mechanical properties of the hydrogel. Moreover, the abundant hydroxyl groups endow the hydrogel with noncovalent interactions, such as hydrogen bonding, and the robustness of the hydrogel was thus improved. NaCl incorporation induced the electrostatic interaction between CNCs and PAA polymer blocks, thus facilitating the improvement of the stretchability of the hydrogel. The as-obtained hydrogel exhibited excellent stretchability, ionic conductivity, mechanical robustness and anti-freezing properties, making it suitable for self-powered sensing applications. A single-mode triboelectric nanogenerator (C-TENG) was fabricated by utilizing the composite hydrogel as electrodes. This C-TENG could effectively convert biomechanical energy to electricity (89.2 V, 1.8 µA, 32.1 nC, and the max power density of 60.8 mW m⁻² at 1.5 Hz.) Moreover, the composite hydrogel was applied for strain sensing to detect human motions. The nanocellulose composite hydrogel can achieve the application as a power supply in integrated sensing systems and as a strain sensor for human motion detection.