This paper studies the relation between the fundamental frequency equivalent impedance of the TCSC and the basic frequency reactance of the TCR, A new concept of equivalent capacitor C/sub T/ of the TCSC capacitor circuit is proposed based on the dynamic simulation experiment of the thyristor controlled series compensator (TCSC), revealing that the equivalent capacitor of TCSC circuit is not a fixed value but varies with control angle /spl beta/. The effect of the fundamental frequency reactance X/sub L/ of TCR on the resonance point and the controlled range is also investigated. The impact on the waveforms and values of current and voltage in the thyristor circuit and the capacitance circuit are analyzed. Both the emulation and dynamic simulation experiment are carried out. The proportion relation between X/sub C/ and X/sub L/ is optimized.