Electroactive sites and crystallinity play a key role to improve the energy conversion performance of piezoelectric polymeric composites. However, these characteristics are attained through time-consuming thermal annealing (TA), which limits the practicality of flexible piezoelectric harvesters (f-PEHs). Here, a short-time plasma annealing (PA) technique was introduced to piezoelectric composite fibers (PCFs) for rapid crystallization and enhanced electroactive β-phase of polymer. The percentage of change in crystallinity of 10-minute PA treated PCF is 20 % compared to TA-treated PCF (annealing time = 2 h), which results in a higher voltage of 2.4 times and current of 3.8 times than the TA-based f-PEH. Finite element analysis confirmed the optimal PA treatment duration and superior performance of PA-treated PCFs. Further PA treated f-PEH was tested for vibration sensor by attaching it to a circulator pipe, confirming its high potential for accurately detecting variations in flow velocity (8–28 L/min). These results demonstrate that PA is an efficient technique for producing high-performance f-PEHs with an increased crystallinity (Xc =22.81 %) in a short time (10 minutes), offering a practical solution for consumer electronic devices and wireless sensors.