Todays, it is well known that using a supplementary controller in FACTS devices can be affective for damping oscillations of electromechanical (EM) mode. In the meantime, appropriate coupling of inputs-outputs signals in the multivariable power system equipped by FACTS can improve the performance of designed supplementary controller. In this paper using of a supplementary controller of interline power flow controller (IPFC) based on input-output signal selection is surveyed to improve power system stability. The proposed controller is added as a supplementary loop to the converter control loops in IPFC and will enhance the damping torque in the power plant by increasing the damping coefficients of the system oscillation modes. Moreover, a solution is provided to use the proposed damping controller in the most optimal path between input-output signals of the system, so that the most controllability on the oscillation modes and the least interference with other channels between the input-output signals are obtained. To increase stability, further Lead-Lag controllers, a novel on-line adaptive controller has been used analytically to identify power system parameters and damp electromechanical oscillations. The simulation results show that the method proposed in this paper not only improves the dynamic stability of the power system but also strengthens the voltage profile.