For direct drive synchronous wind power generation system, the converter of direct drive motor is connected to the stator side of permanent magnet synchronous generator side, through controlling the converter, the maximum wind energy can be captured. Main circuit design of the direct-drive grid-converter is studied. Firstly, power grid side filter is designed and calculated, LCL filter is used instead of traditional L type filter, in this way, the value of the inductance, the volume and cost are reduced effectively, and its inhibitory effect on high frequency signal is more obvious. Not only meet the vector triangle, but also grid connection harmonic current is restrained. Secondly, the filter of motor side is also designed, about the problem of voltage reflection for long cable drive motor PWM converter on the motor side, the solution is to reduce the output value of the du/dt and increase the pulse rise time, at the same time the reflected voltage of the motor side is also reduced. Thirdly ,Brake unit is researched, at the instant of the power grid voltage dips is detected, chopper control is started to IGBT of brake unit, making the machine side power in addition to the net from the side of the part, the rest are consumed in the brake unit, to ensure that the equipment can grid-connected operated. The last but one, the pre-charging circuit is included. Finally, based on the control theory of grid side and wind turbine side and design scheme proposed in this paper, mutual feed experiment is completed based on experiment platform of the 1.5 MW direct drive wind turbine power grid connected converter prototype, the experiment results proved the feasibility of the design method of converter in the pater.