With the advantages of low loss, high efficiency high-speed permanent magnet synchronous motor (HSPMSM) is widely adopted in the flywheel energy storage system (FESS). Structure parameters of the HSPMSM are optimized to achieve higher power and efficiency under the condition of same size. In this paper, a 30kW, 96000rpm HSPMSM is designed and the finite element model is established. From HSPMSM model, the motor is optimized for minimum loss and maximum efficiency. Based on the comprehensive evaluation above the impact on the motor electromagnetic parameters defined by size parameters, the optimal sizes of the motor parameters and the relationship between power, efficiency and size parameters are obtained. The prototype is manufactured and no-load experiment is finished. The result is consistent with the simulation data.