It was always recognized that ac power transmission over long lines was primarily limited by the series reactive impedance of the transmission line. Series capacitive compensation was introduced many years ago to cancel a portion of the reactive line impedance and thereby increase the transmitted power. Subsequently, within the Flexible AC Transmission System (FACTS) initiative, it has been demonstrated that variable series compensation is highly effective in both controlling power flow in the line and in improving stability. In addition, power oscillation is a common dynamic phenomenon which can influence the power system after a disturbance arises. Power oscillation increases the risk of instability and thus reduces the power transfer capacity, particularly in weak transmission lines. In the meantime , solid-state static series FACTS controllers such as SSSC, because of their fast response dynamics, are employed to improve power oscillations damping. The Static Synchronous Series Compensator (SSSC) can improve Power Oscillation Damping (POD) by intelligent modulating of its series reactive power compensation. Furthermore , an SSSC with its energy storage can increase the effectiveness of POD by absorbing the real power from or injecting it into the transmission line. In this paper, the effectiveness of power oscillation damping on the power system stability in presence of SSSC is investigated using a simple power system 500 KV network grid equipped with SSSC rated at 100 MVA connected in series with a transmission line in a Matlab Simulnk environment. The simulation results show a great improvement in power system stability when SSSC with POD is introduced.