A fault warning method of an electric parking brake is provided. The fault warning method includes, a brake is actuated with a motor. An armature current is transmitted from the motor. The armature current is converted to a low frequency current and a high frequency current. A braking force is estimated by the by the low frequency current, and a motor rotating speed is estimated by the high frequency current. The braking force is compared with a predetermined braking force range, and a braking force comparing signal is outputted. The motor rotating speed is compared with a predetermined rotating speed range, and a rotating speed comparing signal is outputted. A determining result is generated by determining the braking force comparing signal and the rotating speed comparing signal. And a warning signal is generated according to the determining result.