The traditional AC network wind farm system has some problems, such as repeated electrical energy conversion, high cost. Aiming at it, A large capacity direct drive wind power unit cascaded DC grid system was designed. The network allowed series interconnection of wind turbines to distributed highvoltage DC (HVDC) power transmission without the AC transformer and the offshore platform. The direct drive permanent magnet power generator (PMSG) and the converter were used in the wind turbine. The converter including the AC/DC unit and the DC/DC unit, and the control strategy has been designed, that was allowed the current to flow at all times in the DC link while simultaneously regulating generator torque by adjusting the duty of the DC/DC unit. The working mode and the control strategy of the landbased thyristorbased inverter power plant had also been developed to realizing the voltage and current regulation of the HVDC link. At last, a complete 150 MW wind farm simulation based on PSCAD/EMTDC was built, and some calculations had been done. The simulation results indicated that the stable operation of the proposed configuration where each turbine was able to independently perform peak power tracking and the robustness and adaptability to the change of wind speed was also good at the same time.