Triboelectric nanogenerators (TENGs) represent an emerging technology in energy harvesting, medical treatment, and information technology. Flexible, portable, and self‐powered electronic devices based on TENGs are much desired, whereas the complex preparation processes and high cost of traditional flexible electrodes hinder their practical applications. Here, an MXene/polyvinyl alcohol (PVA) hydrogel TENG (MH‐TENG) is presented with simple fabrication, high output performance, and versatile applications. The doping of MXene nanosheets promotes the crosslinking of the PVA hydrogel and improves the stretchability of the composite hydrogel. The MXene nanosheets also form microchannels on surfaces, which not only enhances the conductivity of the hydrogel by improving the transport of ions but also generates an extra triboelectric output via a streaming vibration potential mechanism. The measured open‐circuit voltage of the MH‐TENG reaches up to 230 V even in a single‐electrode mode. The MH‐TENG can be stretched up to 200% of the original length and demonstrates a monotonical increasing relationship between the stretchable length and the short‐circuit voltage. By utilizing the MH‐TENG's outstanding stretchable property and ultrahigh sensitivity to mechanical stimuli, applications in wearable movement monitoring, high‐precision written stroke recognition, and low‐frequency mechanical energy harvesting are demonstrated. A flexible and stretchable triboelectric nanogenerator (TENG) with polyvinyl alcohol (PVA) hydrogel encapsulated as electrodes is fabricated. Doping of MXene nanosheets into PVA can greatly promote the electrical properties of the TENG. Utilizing the TENG's outstanding stretchable property and ultra‐high sensitivity to mechanical stimuli, applications in wearable movement monitoring, high‐precision written recognition, and mechanical energy harvesting are demonstrated.