High-power-density induction traction motors have the characteristics of compact structure, high magnetic flux saturation, high operating frequency and high volume loss density. The high operating frequency leads to the significant increase of skin effect and proximity effect of the stator windings. The high frequency eddy current additional loss is generated in the stator windings, causing additional copper loss to increase greatly. Based on the internal harmonic magnetic field theory of the induction motor, the source, calculation method and influencing factors of the stator windings eddy current additional loss are analyzed. A 4-pole 650 kW induction traction motor is analyzed in detail with the finite element method. The stator slot inner magnetic field distribution, the harmonics of the magnetic field in the slot, and the relationship between harmonic amplitude and depth from slot opening are analyzed, and the eddy current additional loss of conductors in the slot is calculated. The calculation results show that the eddy current additional loss of the conductors near the slot opening is the largest, and as the depth from the slot opening increases, the eddy current additional loss of conductors in the slot shows a significant reduction trend. By reasonable design of the stator slot opening depth, the eddy current additional loss of the conductors near the slot opening can be effectively reduced.