In this paper, a piezoelectric energy harvester based on spiral-shaped polyvinylidene fluoride (PVDF) cantilever is designed and fabricated for harvesting low frequency vibration energy in the environment. In this design, the spiral-shaped PVDF cantilever is major for lowering the resonant frequency by increasing the length of the cantilever; Copper and silicon proof masses on both sides are working on further decreasing the resonant frequency and widen its bandwidth. Due to the high flexibility of the PVDF cantilever, this device is extremely sensitive to vibration and can harvest weak vibration energy. Both simulation and experimental results have approved that this device can operate at very low frequency which is about 20 Hz and can effectively harvest energy from 15–50 Hz. The peak of the output voltage can reach 1.8 V with the acceleration of 0.2 g. This is a promising harvester for powering the wireless sensors in the future.