The flexible alternating current transmission devices are becoming important in suppressing power system oscillations and improving system damping. This paper presents effects of STATCOM on damping torque and synchronizing torque in a power system. Base on principle of these two torques controller system is designed. The small signal stability analysis and characteristic of eigenvalues of the system matrix have been used to study the change in electromagnetic torque. Based on the proposed model, the effect of controller is study for three loading conditions (normal, light, and heavy).