A method of preventing an overload current from a power supply to a load through a ground fault circuit interrupter includes the steps of: obtaining an interrupted fault current from a hot wire to a ground wire via a first zero-phase current inductor and a fault current from a neutral wire to the ground wire via a second zero-phase current inductor; amplifying a signal of the fault current by an Op-Amp; and determining the fault current by a programmable control module, wherein when the fault current is larger than a preset threshold, the programmable control module sends a control signal to a control switch such that the control switch electrifies a second coil of a trip breaker to drive an armature at an unlocked position, so as to separate a movable terminal with a fixed terminal for electrically disconnecting the load with the power supply.