Small signal stability mathematical model of directly driven permanent magnet wind power system based on dual PWM converters was established, and the effect on power system stability from parameter variations was researched after wind power system was connected to gird. Some meaningful conclusions were obtained. Maximum power point tracking scheme was applied to wind turbine, and maximum power output was realized in wind power system. Machine side and grid side converters＇ control structure were studied; then a simulation model was built by Matlab. Time domain analysis were performed in different parameters conditions. Results show system keeps good small signal stability in different parameters conditions, theory analysis correctness was proved, which provides useful theory reference for safe and stable connected operation of direct-driven wind power system.