Abstract: When the solid oxide fuel cell (SOFC) operates for a long time at high temperature, due to the repeated start-stop cycle and long-term operation, the reactor is prone to seal failure, which will lead to leakage failure, and then lead to thermal runaway and damage of the reactor, which seriously affects the stability of the system operation. The change of parameters may lead to the occurrence of leakage faults and consequently thermal runaway of the stack or even abnormal system shutdown. Aiming at this fault, a diagnostic method based on the variational mode decomposition (VMD) and Hilbert transform (HT) is proposed through the experiment temperature and voltage signals. This method was applied to experimentally investigate the sealing failure leakage fault in SOFC stacks. The research results demonstrate that utilizing the fault diagnosis method based on VMD and HT can determine the presence of leakage in the stack under open-circuit conditions. By collecting the temperature and voltage signals of the stack and applying this fault diagnosis method, the temperature signal can more rapidly indicate the presence of a leakage fault in the stack. When comparing the diagnosis methods based on Ensemble Empirical Mode Decomposition and VMD, it was found that the latter can detect the leakage fault in the stack 100 seconds faster.