Abstract: Aiming at the problem of some users tampering with the capacity parameters in the transformer nameplate and the factory technical data, a method based on the ratio of additional copper consumption to load losses is proposed to identify the capacity of transformer nameplate. The method can effectively identify whether the capacity of transformer nameplate is real by using only the DC resistance test data and load loss data in the transformer nameplate and the factory technical data. Taking a SFPZ9-130000/220 user transformer as an example, the problem of untrue capacity of the user′s transformer nameplate is discovered in time, and the reliability of the method is verified.