The invention discloses a photovoltaic auxiliary commercial power AC power supply system comprising a solar cell boosting module which provides high voltage DC, a high voltage DC/AC inversion module which converts the high voltage DC and outputs photovoltaic power supply AC having the same frequency and the same phase with those of commercial power, and a power supply module which performs AC isolation and line combination on the commercial power and the photovoltaic power supply AC and the supplies power to a load. The AC isolation and line combination power supply module comprises a one-way coupling isolation control circuit which is connected with the commercial power and provides commercial power AC to the load at the output end. The photovoltaic power supply AC and the output end of the one-way coupling isolation control circuit are connected in parallel and then supply power to the load together. The one-way coupling isolation control circuit only allows passing of the commercial power and prevents the photovoltaic power supply AC from feeding into the commercial power grid. The photovoltaic auxiliary commercial power AC power supply system is simple and reasonable in structure, low in manufacturing cost without storage battery and pollution-free to the environment so that the reactive current of the load can be prevented from entering the commercial power grid.