In development of a flywheel energy storage system, electric power loss reduction is expected by using superconducting bearings. However, for realization of superconducting bearing strong levitation force, rotation loss reduction and axial descent reduction are required. It is known with axial descent reduction technology that a preload method is effective, whereas by this method, the levitation force becomes quite small compared with the normal levitation. We confirmed the performance of the preload method by experiment using a YBCO superconducting electromagnet. The preload method is improved and a method, which does not change the rate of the force relaxation and makes the levitation force larger than the existing preload method is proposed.