Wearable instruments are functional devices that can be worn on human body, sensing, transmitting and processing body or environmental information in real time, and show broad application prospects in medical health, especially artificial intelligence, sports and entertainment. With the development of wearable instruments, various flexible sensors have emerged. Flexible mechanical sensors based on piezoelectric effect have attracted much attention because of their advantages of wide sensing frequency, fast response, good linearity, and self-power supply. However, traditional piezoelectric materials are mostly brittle ceramics and crystalline materials, which limit their application in flexible devices. With the deepening of research, more and more flexible piezoelectric materials and piezoelectric composites continue to emerge, injecting new development vitality into flexible wearable mechanical devices. This article mainly summarizes the cutting-edge progress of flexible wearable piezoelectric devices, including piezoelectric principle, preparation and performance improvement methods of flexible piezoelectric materials. In addition, the main application directions of flexible wearable piezoelectric devices, including medical health and human-computer interaction, as well as the challenges and opportunities encountered, are summarized.