The DFIG-wind turbine, can create the potential instability to the existent power grid, equivalently presenting itself as a random voltage source with its dynamic impedance, which has the implicit and varying electrical characteristics with the changeable rotor speed. Thus, it inevitably leads to the mutual interaction between DFIG-wind turbines themselves and dynamic custom loads. This paper studies the closed-form impedance analysis of a practical DFIG-wind turbine system. A small-signal model of the DFIG system in the dq-frame is developed with respect to discrete rotor speeds using the impedance-based approach. Moreover, a practical testing method is adopted to facilitate the verification of the impedance modeling.