Thyristor controlled series compensation（TCSC） can be used to improve conveying capacity of long distance and weak contact power system， damp low-frequency oscillation and improve stability of power system. TCSC can produce more useful effect with reasonable control policy. The control strategy of Cheng-Bi line 220 kV TCSC system is designed mainly for the two stages of power system transient stability and damping oscillation. The controller is composed of impedance control component element， damping control component element， transient stability control component element， protection component element and time delay component element. System field test demonstrates that Cheng-Bi line 220 kV TCSC system can adjust impedance smoothly and quickly， damp the low frequency oscillation effectively and improve system stability greatly.