Flexible and wearable electronics have presented a wide range of advantages to non-invasive real-time human health monitoring. However, its remarkable energy consumption during continuous and long-time operation brings essential, practical challenges, which lead to growing recognition of exploring new and efficient energy strategies for wearables. Here, inspired by human joints as a biomechanical energy source that shows an ideal option for sustainable powers, we design a battery-free sweat sensing system integrated with sweat resistant selfsustainable energy supply and wireless communication interface, where piezoelectric nanogenerators (PENGs) efficiently converting biomechanical energy from freely movable joints (finger, cubital fossa and popliteal space) into electricity serving as the self-powering module. Physiological relevant parameters in sweat, including Na+ , K+ and pH, are sensed and wirelessly transmitted to the user interface via Bluetooth communication. This system shows a paradigm of wearable electronics driven by human joints that demonstrated efficient self-sustainable energy supply and multiplexed physiological detection.