Flexible sensor systems have paved the way for development in the field of next-generation flexible electronics, as traditional micro/nanoscale manufacturing processes cannot meet the requirements of industrial production for particular structures and materials. In this paper, a high-performance, flexible, and ultrastretchable piezoelectric sensor is realized with the help of an electrohydrodynamic direct-writing technology. The sensor is used directly for monitoring human body movements, breathing, and other actions, and outputs a stable and consistent electrical signal. At the same time, the design and application of a flexible piezoelectric organic thin-film transistor (OTFT) sensor system are realized using a flexible OTFT device prepared using an electrohydrodynamic direct-writing technology. The system produces a signal with very high magnification (1000 times) compared with the original signal and solves the conventional problems of a weak output signal and susceptibility to interference. The flexible piezoelectric OTFT sensor system can thus effectively monitor the speed of a human joint movement, stride frequency, and so forth, demonstrating its practical applicability.