The basic principle and working characteristics of bearingless permanent magnet synchronous motor are expounded systematically. The variation characteristic curves of output traction torque, x-axis and y-axis levitation force with initial angle under the coupling excitation of rotor permanent magnet, traction current excitation and levitation current excitation are analyzed. The variation law of unilateral magnetic tension under different eccentricity in x-axis and y-axis directions is studied and verified by finite element simulation. The results show that the eccentricity of y-axis direction will increase the periodic average value of unilateral magnetic tension in the y-axis direction and the dynamic amplitude fluctuation in both x-axis and y-axis directions. With the increase of the eccentric distance in the y-axis direction, the average value and amplitude of the unilateral magnetic tension in the y-axis direction increase linearly, while the average value of the unilateral magnetic tension in the x-axis direction is approximately 0, and the amplitude increases linearly. The coupling excitation of rotor permanent magnet, traction and levitation winding current will produce rotating traction force and x-axis and y-axis levitation force. As long as the levitation force generated by the position of x-axis and y-axis is compensated in reverse, so that the combined force of the motor rotor in the directions of x-axis and y-axis is 0, the rotor can operate in a non-eccentric state during the rotation of the motor.