The embodiment of the invention provides a fault diagnosis method, a device and a follower diagnosis system, and relates to the technical field of new energy automobiles. The method comprises the following steps of: receiving first fault information sent by the engine management system and second fault information sent by a generator control unit; generating system assembly fault information according to the first fault information, the second fault information and the third fault information of the power follower controller itself; obtaining a system fault level according to the fault information of the system assembly; generating an execution instruction corresponding to the system assembly fault information and the system fault level. The embodiment of the invention is from the perspective of the system, aggregating the first fault information and the second fault information according to the system angle, realizing and sharing the resource coordination, and performing redundant processing, mutual verification, and comprehensive analysis, try to find out the real cause of the fault, and adopt an optimal processing strategy to achieve system fault handling.