Fuel cell DC/DC device and hydrogen energy train fuel cell system

The invention provides a fuel cell DC/DC device and a hydrogen energy train fuel cell system. A fuel cell DC/DC device comprises: a Buck/Boost module, the low voltage side of which is connected with a fuel cell and an auxiliary machine, and the high voltage side of which is connected with a DC bus; the high-voltage side pre-charging loop is connected between the Buck/Boost module and the direct current bus; wherein the Buck/Boost module is switched to a Buck working mode after pre-charging of the high-voltage side pre-charging loop is completed, so that voltage passing through a direct-current bus is reduced into power supply voltage needed by an auxiliary machine, and a fuel cell is started; and the Buck/Boost module is switched to a Boost working mode after the fuel cell is started, so that the output voltage of the fuel cell is boosted to the direct-current bus voltage to supply power to the load, and meanwhile, the output voltage of the fuel cell also provides power supply voltage for the auxiliary machin