The invention discloses a single-degree-of-freedom magnetic-levitation rotor supporting system. The single-degree-of-freedom magnetic-levitation rotor supporting system is composed of radial magnetic-levitation bearings arranged on the upper portion of a motor spindle and prestressed magnetic-levitation composite bearings arranged on the lower portion of the motor spindle. A stator part magnetic ring of the corresponding radial magnetic-levitation bearing in each prestressed magnetic-levitation composite bearing on the lower portion of the spindle and a stator part magnetic ring in a repulsive radial-axial magnetic-levitation bearing are arranged on the same stator base disc, and the stator base discs are fixedly connected with a machine shell. A rotor part magnetic ring of the corresponding radial magnetic-levitation in each prestressed magnetic-levitation composite bearing on the lower portion of the spindle and a rotor part magnetic ring of the corresponding repulsive radial-axial magnetic-levitation bearing are arranged on the same rotor base disc (209) jointly, and the rotor base discs are fixedly connected with the spindle. Mechanical protective bearings (212 and 213) matched with a sliding pair are arranged between the upper end of the spindle and an upper end cover of a motor as well as between the lower end of the spindle and a lower end cover of the motor.