The dynamic result of static synchronous series compensator is presented in this paper. A voltage source inverter equipped with a dc source is used as an SSSC (static synchronous series compensator) to examine the effect of this device in controlling the power flow through transmission line. This device works not only as a reactive power compensator but has the ability of supplying and absorbing active power from the transmission line. In control system of SSSC two closed loops are used for both active and reactive power. In addition to reactive power compensation, SSSC also provides voltage profile improvement in system. Simulation results for different conditions are also described.