The invention discloses a safe operation method of active voltage reduction for a ground fault phase of a non-effective grounding system, and the safe operation method is applied to the ground fault safe operation of a neutral point non-effective grounding generator or power distribution network. When a single-phase ground fault occurs, an adjustable current source is applied additionally between a bus at a non-effective grounding system side and the ground, or between a circuit and the ground, or between a neutral point and the ground, or between a shunting tap at a transformer non-effective grounding system side winding and the ground, to adjust the injected current magnitude and phase and further reduce the fault phase voltage, so that the fault point voltage is lower than the ground arc continuous combustion voltage to meet the long-term non-stop safe operation requirement. According to the invention, the fault phase voltage is reduced to a non-zero safe operation value, so the permanent single-phase earth fault current is suppressed, the rising amplitude of the non-fault phase voltage is limited, the risk of non-fault phase insulation breakdown is reduced, the personal safety and equipment security risks are reduced, the occurrence of power outages is effectively prevented, and power supply reliability and security are greatly improved.