Abstract:in recent years, with the rapid development of wind power unit capacity, in order to maintain the safe and stable operation of power system and to ensure the safety of wind power grid, it is necessary for wind farms to ask for low voltage across. The low voltage crossing requirement is the need of power balance and frequency stability of power system, and it is also the need of voltage stability and voltage recovery of local grid. In order to minimize the impact of large-scale wind power access system on the power grid, higher requirements are put forward for wind power units, namely, the wind power unit has certain low voltage crossing capability. The basic structure of the variable speed constant frequency doubly-fed wind turbine is introduced, and a dynamic mathematical model is established. Based on Matlab/Simulink simulation application platform of the system simulation model, combine with the low voltage across the wind farm capacity requirements of relevant standards, according to different grid voltage drop, the simulation application research on the variable speed constant frequency wind turbines ability of low voltage through the simulation results show that the doubly-fed wind power generator in the power grid voltage drop when meet continue to parallel operation conditions, and to provide reactive power to the grid voltage recovery, to provide the size of the reactive power related to the degree of power grid voltage sags.