Abstract: This paper proposes a concept of equivalent electric exchange. That is,the surplus power will be output to the grid as a type of hypothetical energy storage when the photovoltaic power is sufficient over the basic demand, otherwise,the surplus power of hypothetical energy storage will be input from the grid for hydrogen production when the photovoltaic power is insufficient over the basic demand for the stable hydrogen production. So that,the installed capacity of water electrolysis equipment will be reduced,and the effective utilization time of water electrolysis equipment as well as the proportion of photovoltaic power for hydrogen production will be increased,resulting in the investment of water electrolysis equipment reduced. Furthermore,the actual output curve of photovoltaics is given to expound the significance of equivalent electric exchange in the design of photovoltaic hydrogen production project.