Abstract: The bottleneck in the rapid development and widespread deployment of the Internet of Things (IoT) is how to power tens of thousands of sensor network nodes in an efficient and cost-effective way. The conversion of vibration energy into electrical energy for self-powering of the sensor is a very feasible solution. However, low-frequency components make up a large proportion of environmental vibrations, and traditional vibration energy harvesting methods have difficulty in efficiently converting low-frequency ( < 10 Hz) vibration energy, which limits the widespread use of vibration energy harvesting technology in the field of IoT. In this paper, a quasi-zero-stiffness-enabled piezoelectric vibration energy harvester (QZSE-EH) is proposed for the harvesting of the ultra-low frequency energy from the environment, human body and some mechanical devices. At first, the electromechanical coupling equation of the energy conversion unit is obtained by using the energy method, and the dynamic and electrical response equations are solved by using the harmonic balance method. The effect of the damping ratio and the excitation amplitude is explored by means of the results of the analytical solution. Finally, a prototype of the QZSE-EH was fabricated and the experiment was carried out to verify the correctness of the dynamic and electrical output response of the system. The results show that when the frequency is 2.5 Hz, the maximum peak voltage of a single energy conversion unit in the QZSE-EH reaches 25 V. The QZSE-EH proposed in this paper is expected to overcome the problem that the operating bandwidth of conventional resonant piezoelectric energy harvesters depends on the natural frequency, and the multi-stable energy harvesters are unable to cross the barrier, making ultra-low frequency and low-amplitude energy harvesting extremely difficult. This paper provides a new idea for the efficient harvesting of ultra-low frequency and low-amplitude vibration energy, and can further consolidate the theory of vibration energy harvesting.