Based on the research on characteristics of the recovery voltage of the opened phase when a transient single-phase fault occurs on a shunt reactor compensated transmission line， quantitative analysis is performed on the transient components of the recovery voltage by s -domain analysis. The cause of the decaying periodic component of the recovery voltage is revealed. Based on the comparison between the wave form of the terminal voltage of the faulted phase of a transient fault and that of a permanent fault， a criterion for identifying the magnitude of the decaying periodic component of the terminal voltage on the opened phase caused by the permanent single-phase fault is proposed and a practical method for extracting the magnitude is presented. The method is simple and fast， and not subject to the influence of transition resistance. It can be applied to fault nature identification in an adaptive single pole auto-reclosure scheme for transmission lines with shunt reactor compensation and selection of proper reclosure time instance.