Vector control strategies based on the dq model are widely used in the doubly fed induction generator（DFIG） wind turbines. Normally it is divided into before and after grid integration modes to analyse. This paper establishes a unified model of before and after grid integration， which combines the DFIG rotor equations and the proportional integration（PI） controller into a four-order model. The impacts of the rotor current controller's parameters on the system are analyzed. The parameter design principle and methods are also introduced in details. Simulation results prove the proposed method.