In order to analyze the stability of variable speed wind turbine generator system under different grid frequencies，an electromagnetic transient model of small signal stability analysis for a doubly-fed wind turbine is proposed.The model considers the grid frequency variations.Firstly，literature review shows that the conventional electromagnetic transient model of doubly-fed induction generator（DFIG）cannot reflect grid frequency disturbances due to lack of grid frequency reciprocal items.As such，an improved expression of rotor transient electromotive force is proposed and the small signal improved model of DFIG with its converter control system is established considering the grid frequency disturbance impacts.Then，eigenvalues are calculated and compared by using the improved and traditional electromagnetic transient model under different grid frequencies.Finally，the time-domain simulation model considering grid frequency disturbances is established，and then the active power and the rotor speed performances are simulated under different grid frequencies and different load disturbances.Analytical and simulation results show that compared with the traditional DFIG electromagnetic transient model，the improved model is more sensitive to the grid frequency change，and can be adapted to analyze the stability of doubly-fed wind turbines considering the grid frequency variations.