The invention discloses a method for manufacturing the insulation structure of a single rotor winding bar and belongs to the field of AC excitation generating motor rotor winding manufacture. The exciting voltage of a large generator rotor is usually less than 500V and the exciting current of the large generator rotor is direct current. A large AC excitation generating motor, however, performs excitation by using alternating current and has high exciting voltage. The high-voltage AC excitation increases current losses in the rotor winding bar and has a high requirement for the main insulation of the rotor winding bar. In order to solve a problem caused by the high-voltage AC excitation, electromagnetic wires are designed. The electromagnetic wires are subjected to transposition weaving and filled with transposition insulation, inter-row transposition, and cover insulation, and then are subjected to heating, pressurization, and solidification on a wire hot pressing mold to form a rotor winding bar wire. The rotor winding bar wire is wrapped in a mica tape and is subjected to heating, pressurization and solidification on a winding bar hot pressing mold to form rotor winding bar main insulation. The rotor winding bar with such insulation structure may effectively reduce eddy current loss. The main insulation solidified by the mica tape completely satisfies requirements of the rotor winding bar for electrical performance, mechanical performance, thermal performance, and operation environment.