The invention relates to a mutual inductor detection device, particularly relates to a polarity detection device for metering mutual inductor secondary loop, aims to solve problems in the prior art and aims to substantially improve safety through arranging telescoping crimping clamps to prevent from stretching hands into a high voltage metering cabinet for work during detection. The detection device comprises a box body, wherein the box body comprises a storage battery fixed in the box body, wire rollers which are symmetrically arranged at two sides of the storage battery and are used for accommodating leads, and handle slots used for fixing the telescoping crimping clamps, the two telescoping crimping clamps comprise handle portions arranged corresponding to the handle slots, telescopingportions used for controlling the clamp for telescoping, and clamp ports used for clamping a measurement end, corresponding sides of the two handle portions are connected with the leads, and the leadsare connected with positive and negative electrodes of the storage battery after wire roller winding.