<p>In urban rail vehicle operations, the supercapacitor box is critical in the energy storage and power supply system. Despite considerable research on the fatigue characteristics of lithium batteries, simulation studies of the fatigue performance of energy storage supercapacitor boxes under random vibration loads are scarce. This study assesses the fatigue characteristics of the supercapacitor box in rail vehicles under random vibration conditions to provide theoretical support for structural optimization and reliability design. A supercapacitor box of a rail vehicle was taken as the research object, and its refined finite element model was established. The first ten modes were calculated, which showed that the frequencies exceeded 30 Hz, indicating that the supercapacitor box was unlikely to resonate. Through random vibration analysis, the weak position was identified, and the maximum stress was calculated to be 85.17 MPa. The fatigue characteristics in the frequency domain under random vibration, defined by the power spectral density (PSD), were analyzed, and the number of fatigue cycles to failure of the vehicle-mounted supercapacitor box was approximately 10^4.522. The research results provided a crucial theoretical foundation for the structural optimization and reliability design of supercapacitor boxes for rail vehicles.</p>