As the parameter characteristics of compact transmission lines are quite different from those of conventional transmission lines， a study of their influence on sub-synchronous resonance（SSR）， the advantages and disadvantages of some series-compensated compact transmission lines for the heat-engine plant is of practical significance. With the transmission scheme of Shangdu Plant ProjectⅡ as our background and adopting the method of eigenvalue analysis， an investigation is made on the SSR in the compact transmission lines， conventional transmission lines and high surge-impedance-loading compact transmission lines. The results show that compact transmission lines are capable of providing a wider range for a SSR-free series compensation ratio than conventional transmission lines. What with the impedance of only 73% of the conventional transmission lines， compact transmission lines have good prospects for application in choosing appropriate compensation schemes and preventing SSR by TCSC.