A novel field modulated magnetic gear (FMMG) with concentric configuration was proposed and introduced to the drive train for a wind turbine system, which eliminated the vibration, noise and lubrication problems of mechanical gearbox and avoided the size and weight issues of directly-driven wind turbines. And the efficiency and reliability were improved simultaneously. Based on the field computations by time-stepping finite element analysis, the co-simulation FEM model of synchronous generator and magnetic gear was established and the dynamic performance of the transmission system was studied. The electromagnetic design and simulation results were verified by the experiment of the 1 kW FMMG prototype.