A hydrogen pressure maintenance system of a hydrogen fuel engine includes a hydrogen tank configured to store hydrogen, an injector configured to inject the hydrogen, a hydrogen internal combustion engine configured to operate using the hydrogen from the injector, a hydrogen pressure controller configured to supply the hydrogen to the injector by controlling a pressure of the hydrogen supplied from the hydrogen tank, a hydrogen pressure intensifier device configured to increase the pressure of the hydrogen and supply the hydrogen to the injector, a hydrogen pressure sensor configured to measure the pressure of the hydrogen and output a signal based on the measured pressure of the hydrogen, a hydrogen bypass valve configured to control the hydrogen to be supplied to the injector through the hydrogen pressure controller or to the injector through the hydrogen pressure intensifier device, and a controller configured to control the hydrogen bypass valve according to the signal from the hydrogen pressure sensor.