The invention provides a fault diagnosis method for a fuel 
cell system. The fault diagnosis method comprises the steps of executing offline 
processing and executing on-line 
processing; the off-line 
processing is used for establishing a fault 
database according to operation and fault data of a fuel 
cell, collected by a plurality of sensors and calculating a fault threshold value; and the on-line processing is used for identifying the type of a fault according to the fault 
database and the fault threshold value, judging the type of the fault according to the fault 
database, if the fault is reversible and a fault component is a non-
core component, reconstructing a sensor 
signal corresponding to the fault component to enable the fuel 
cell system to continue running, and if the fault is irreversible or the fault component is a 
core component, shutting down and maintaining the fuel 
cell system. The method has the advantages that 
signal authenticity 
verification, fault diagnosis, fault positioning and fault-tolerant control are realized, and 
signal reconstruction is realized through an 
algorithm to maintain 
power output in a fault state, so that the safety and reliability of the fuel cellsystem for a vehicle are ensured; and the method can be suitable for different fuel cell systems.