Based on transient models of series compensated lines and parameter identification principle，a new distance protection method for series compensated lines is proposed.The protection uses transient fault information to calculates the inductance of series compensated lines which can correctly reflect the distance from fault point to relay location，so it can overcome the overreach problem for external faults.Moreover，the fault point relative to series capacitor compensating location is turned to an unknown evaluated variable.The unity of protection algorithm is implemented when faults occur in front of series capacitors or behind them，so there is no need to identify the fault location relative to series capacitors in advance and no need to cooperate with traditional protection.Since only the transient data before mental oxide varistors（MOV）conduction is used for identification process，MOVs nonlinear characteristic neednt to be considered in this method.Because only single terminal electric quantities are used，the protection is easy to be realized without using communication channels.The simulating results show the validity and adaptability of the protection principle proposed.