The utility model relates to a special winding wire for a traction transformer of a standard motor train unit. The special winding wire comprises a flat wire conductor, an attached insulating layer, amain insulating layer and a reinforced insulating layer, wherein an attached insulating layer is fixed on the outer surface of the flat wire conductor, a main insulating layer is fixed on the outer surface of the attached insulating layer, and a reinforced insulating layer is fixed on the outer surface of the main insulating layer; the cross section of the flat wire conductor is in the shape of arounded rectangle, and the length-width ratio of the rounded rectangle is 2: 1-8: 1. According to the utility model, the continuous reliability of the winding wire insulating layer is improved, and the design and use requirements of the standard motor train unit traction transformer winding are met.