Abstract: The present disclosure belongs to the technical field of hydrogen production by water electrolysis, and relates to an energy optimization heat pump system and method for hydrogen production by water electrolysis with low-pressure ratio. It includes a hydrogen oxygen gas-liquid separation unit, a heat pump compressor, and an expander. The hydrogen oxygen gas-liquid separation unit is connected to the hydrogen dryer through a hydrogen cooler. The hydrogen oxygen gas-liquid separation unit is connected to the heat pump absorber through a circulating cooling water pipeline, the hydrogen cooler is connected to the refrigerator through a refrigerant pipeline, and the hydrogen dryer is connected to the steam generator through a hot water pipeline and a steam pipeline respectively. The present disclosure is conducive to reducing the pressure ratio of the heat pump compressor, enriching the selection range of heat pump working fluids, and improving the energy utilization rate of the system.