Doubly-fed wind turbines have many control loops that are coupled to the sub-synchronous oscillation frequency range, which may lead to Sub-Synchronous Control Interaction (SSCI) between the control loop and series compensated transmission line. Although inner loop proportional parameter has a significant effect on the SSCI, because of the limit of stability threshold, it is necessary to find out the effects of other parameters in the control loop on the SSCI. On the basis of the establishment of the impedance model contains control loops of DFIG, bode plot and sensitivity analysis are adopted to compare the influence of different controller parameters on the system impedance and frequency scan is used to reveal the impact mechanism of system impedance at different control parameters. The results show that the integral parameter of the rotor side directly affects the resonance frequency and series compensation degree of the transmission line. The reduction of the integral parameter can increase the adjustable range of the proportional parameter, which is beneficial to reduce the risk of SSCI in grid-connected system. This work is supported by International Cooperation Project of Sichuan Provincial Science and Technology Department (No. 2015HH0055).