The invention relates to a power supply protection circuit for a hard disk. The power supply protection circuit comprises a switching circuit, a sampling circuit, a comparison circuit and a time-delay circuit. The switching circuit is connected between a hard disk power supply and the hard disk and is used for controlling whether the hard disk power supply is output to the hard disk or not. The sampling circuit is used for sampling a voltage value which is output to the hard disk by the hard disk power supply. The comparison circuit is used for receiving the voltage value obtained by the sampling circuit, comparing the sampled voltage value with a standard voltage value and controlling the switching circuit to be switched on or switched off according to a comparison result. The time-delay circuit is connected between a system power supply and the enabled end of the comparison circuit and is used for enabling the comparison circuit to output an electric level signal after output of the system power supply and before output of the hard disk power supply so as to keep the switching circuit at an on state. The power supply protection circuit for the hard disk can be used for stopping supplying power to the hard disk when the voltage value is too high so as to protect the hard disk.