A power supply protection device including a driving circuit, a logic control unit and a protection module is provided. The driving circuit adjusts an external voltage according to a first driving signal and a second driving signal and outputs a driving voltage. The logic control unit generates the first driving signal and the second driving signal according to a protection signal and a pulse signal. The protection module outputs a plurality of test currents orderly to detect a plurality of impedances of the driving circuit before the driving circuit receives the external voltage, generates a plurality of voltage signals according to the impedances and compares the voltage signals with a plurality of reference voltages to generate the protection signal. A power supply protecting method for protecting a driving circuit is also provided.