The invention discloses a method for detecting semiwave direct current, which overcomes the defects of the conventional direct current detection method and has the advantages of simplicity, convenience, practicability and the like. The method comprises that: 1) when a power distribution system has a singlephase earth fault, the neutral voltage of a grounding transformer is set to be sinusoidal signals with the power frequency of 50Hz; 2) a direct current generator is subjected to siliconstack half wave rectification to generate direct current, the direct current is semiwave direct current which is also called pulsating direct current and is injected to the fault power distribution system, and direct current signals are wire selecting and positioning judgment signals to be detected; and 3) according to the electromagnetic field principle, the semiwave direct current generates a magnetic field, so the semiwave direct current can be detected by detecting the magnetic field generated by the semiwave direct current.