A high efficiency axial-flux brushless DC motor assisted by self axial magnetic bearing and used in flywheel energy storage system is proposed in this paper. In this design, the rotor with composite rim acts as the flywheel of the system and is sandwiched between two disk type stators which are made of amorphous metal to reduce iron losses. The dual-stator machine combines the functions of axial flux brushless DC motor and axial magnetic bearing to rotate the flywheel-rotor and levitate it in vertical orientation. The other four degrees of freedom in radial directions are constrained by ceramic ball bearings for simple operation, high efficiency and long life span. Optimized design approaches are employed to achieve low losses, and high power density. Three-dimensional FEM analyses are implemented, and the analysis results support the feasibility of the proposed motor.