The operating environment of high-speed train axle boxes, combined with the unavailability of embedded power solutions, poses significant obstacles for condition monitoring. The installation of sensing infrastructure in energy limited areas is often impractical, limiting the performance of connected monitoring systems. Therefore, there is a growing need to innovate methods for capturing ambient energy during train operation, enabling autonomous monitoring systems for these components. Based on it, we introduce a self-contained vibration energy harvesting system tailored for high-speed train axle boxes. The system captures ambient vibrations from the surrounding environment and converts them into electrical power to support monitoring equipment. Advanced energy storage and management components are integrated to guarantee a continuous, reliable power supply for onboard sensors. The experimental data demonstrates that the system reaches a maximum power output of 26.36 mW at a frequency of 20 Hz and an amplitude of 5 mm. In continuous operation, the energy storage part is completely charged in 40 h through vibration energy harvesting, while also maintaining uninterrupted sensor functionality. By eliminating the reliance on external power sources or frequent battery changes, this system significantly improves the sustainability and reliability of condition monitoring for high-speed train axle boxes.