The embodiment of the invention discloses a vehicle fuel cell DC-DC converter and a vehicle power system, and relates to the technical field of the vehicle power system. The vehicle fuel cell DC-DC converter comprises an inverter circuit, an isolated voltage transformation circuit and a rectifier circuit. The input end of the inverter circuit is connected with the output end of a fuel cell and used for converting the direct current outputted from the fuel cell into alternating current. The input end of the isolated voltage transformation circuit is connected with the output end of the invertercircuit and used for isolating the circuit on the primary input side of the isolated voltage transformation circuit from the circuit on the secondary output side. The input end of the rectifier circuit is connected with the output end of the isolated voltage transformation circuit and used for converting the alternating current into the direct current to be outputted. The vehicle fuel cell DC-DCconverter is suitable for the new energy electric vehicle.