The invention provides a photovoltaic DC power supply system and a method for electrolytic aluminum electrolytic production. The system comprises a photovoltaic power generation module, a fuel cell energy storage module, a space-time heterogeneous coupling controller and a power grid power supply module, wherein the photovoltaic power generation module provides DC power for an electrolytic aluminum electrolytic bath and charges the fuel cell energy storage module; the fuel cell energy storage module stores remaining power of the photovoltaic power generation module, and a stored gas is adopted as a fuel to obtain power to provide power for the electrolytic aluminum electrolytic bath; the power grid power supply module provides power for the electrolytic aluminum electrolytic bath; the space-time heterogeneous coupling controller selects a power input side of the electrolytic aluminum electrolytic bath according to the relationship between the photovoltaic power generation maximum power Ps of the photovoltaic power generation module and the rated power P0 of the electrolytic aluminum electrolytic bath; and according to voltage at different input sides and the rated voltage U0 of the electrolytic aluminum electrolytic bath, a needed duty cycle is calculated, and the output voltage at the power input side is controlled. The system relieves the power supply pressure and the peak regulation pressure of the power grid, and consumption of fossil energy is saved.