An over-voltage protection system is connected between a power supply and two working circuits of an electronic device, and includes a first over-voltage protection circuit, a second over-voltage protection circuit, and a voltage load circuit. The over-voltage protection system detects voltage of the power supply, isolates the power supply from a first working circuit when the power supply exceeds a first predetermined voltage value, and isolates the power supply from a second working circuit when the voltage of the power supply exceeds a second predetermined voltage value and is lower than the first predetermined voltage value. The voltage load circuit bears partial voltage of the power supply to provide necessary power to the second working circuit when the voltage of the power supply exceeds a second predetermined voltage value and is lower than the first predetermined voltage value.