Firstly, based on the equal circuit of power grid with doubly fed induction generators (DFIG), the paper studies the frequency components of short circuit voltage and current in the place where the protection devices are equipped with. And the analyzing result leads to different frequency characteristics of voltage and current for wind farms during faults. Secondly, simulations based on Matlab/Simulink verifies the particular characteristics and yields the relationship between transition fault impedance and the characteristics of short-circuit voltage and current. Following the frequency’s feature of short circuit current, the reliability and adaptability of distance protection are analyzed. Finally, simulation results verify the adaptive failings of this traditional protection in wind farms, and the results also have some certain instructional significance to relay protection test.