Simplified equivalent circuit and its changed form, DC voltage regulation factor, equilibrium current and voltage of 12-pulse traction rectifier transformer with axial double split winding structure are discussed. The equilibrium current and increased factor of the winding capacity due to the equilibrium current are analyzed emphatically. Reasonable parameters of the transformer are determined and the problem that the two-bridge rectifier circuit in parallel composed of this kind of transformer is operated without interphase reactor is also explained.