The invention discloses a new energy automobile fuel cell system, a working method, a hydrogen inlet flow calculation method and an efficiency evaluation method, Belongs to the technical field of newenergy. Keys points of the new energy automobile fuel cell system are that the new energy automobile fuel cell system comprises an air supply system, a hydrogen supply system and a fuel cell stack, wherein the air supply system provides fresh air for the fuel cell stack, and the system comprises an air filter, a centrifugal air compressor, a gas heat exchanger, a humidifying and intercooling assembly, a throttle valve, a water segregator, a drain valve, a turbine and a back pressure valve; the hydrogen supply system provides fresh hydrogen for the fuel cell stack and comprises a hydrogen tank,a pressure reducing valve, an ejector, a water distributor, a water distribution valve, a nitrogen discharger, a nitrogen discharge valve, a first one-way valve, a circulating pump and a second one-way valve; and the fuel cell stack is a place where hydrogen and air react, and chemical energy is converted into electric energy to provide kinetic energy for accessory mechanisms and loads. The invention aims to provide the new energy automobile fuel cell system, the working method, the hydrogen inlet flow calculation method and the efficiency evaluation method, the stability of the fuel cell isimproved, and the efficiency of the fuel cell is conveniently calculated and evaluated.