The utility model discloses an onsite detector for the metering characteristic of a merging unit, belonging to the field of metering detection in the intelligent electrical network. The merging unit (100) to be detected, a TV secondary loop (200), a TA secondary loop (300), a synchronized clock (400) and a digital fiber electrical energy meter (500) are included; the onsite detector is also provided with an onsite detection unit (600) of the merging unit; and the merging unit (100) to be detected, the TV secondary loop (200), the TA secondary loop (300), the synchronized clock (400) and the digital fiber electrical energy meter (500) are all connected with the onsite detection unit (600) of the merging unit. The detector detects the ratio and angular difference sampled by the merging unit at interval without power failure, errors of the merging unit is thus effectively controlled, and the accuracy and effectiveness of a metering system in an intelligent transformer station are ensured.