Aiming at a large amount of wind farms increased from 220 kV to 750 kV grid，the dynamic process of voltage and frequency problems in regional power grid and main power grid is studied after off － grid of large － scale wind turbine units， and the stability control strategy is put forward after simulation analysis with PSASP program． The calculation results show that the voltage fluctuation of substation bus is proportional to the capacity of wind power area． Dynamic reactive power compensation equipment is installed in substation with large voltage amplitude，and the voltage increase of the variable bus is effectively controlled．