The invention discloses a portable multipoint grounding detector used for detecting that whether multipoint grounding exists in a mutual inductor common loop or not. The portable multipoint grounding detector comprises a constant flow source used for outputting current to the neutral conductor of the mutual inductor common loop, a current transducer used for detecting the grounding current of the common grounding point of the mutual inductor common loop and outputting a grounding current value, a voltage transducer used for detecting the voltage to ground of the common grounding point of the mutual inductor common loop and outputting a voltage to ground value, a keyboard used for receiving a setting parameter set by a user and a CPU used for receiving the grounding current value, the voltage to ground value and the setting parameter. According to the invention, whether the multipoint grounding exists in the mutual inductor common loop or not can be detected rapidly and conveniently, and when detection is conducted, both time and labor are saved, and the effect is relatively good.