Abstract: Air leakage is a common fault in proton exchange membrane fuel cell (PEMFC) system, and the occurrence probability will gradually increase with the increase of system running time. This kind of fault will directly affect the performance of PEMFC. Therefore, a fault-tolerant control strategy based on adaptive slide mode observer (ASMO) is proposed. The leakage of the air compressor is compensated by the reconstruction of the air flow observer. At the same time, an iterative adjustment algorithm of the opening of the back pressure valve is designed to control the air supply pressure, ensure a stable and appropriate air supply, and avoid the phenomenon of "oxygen starvation" in the stack. Finally, the observer and fault-tolerant control strategy are verified and analyzed on the model in the loop (MIL) platform. The results show that the adaptive sliding mode observer has better convergence speed and estimation accuracy than the traditional sliding mode observer. After adopting the fault-tolerant control strategy based on adaptive sliding mode observer, the system can restore the normal air supply after fault, and improve the overall reliability of the system.