We investigated the optimum design for magnetic flux distribution of a superconducting flywheel energy storage system (SFES) using the Maxwell 3D program. A rotor was composed of the laminated structure by permanent magnets and iron, and a stator consisted of bulk type superconductors. To simulate, we assumed that the bulk type superconductors has the behaviors of type I superconductor. We designed the rotor to adjust one or two iron into the center or trisection points of superconductors. The interval between the superconductor and the permanent magnet is 5 mm. We observed that a rotor with two iron pieces in the magnet stack placed to coincide with the middle of the bulks generated a more uniform magnetic field than one with a single iron piece located to coincide with the top of the bulks.